Holographic Wide Angle Display

ABSTRACT

An apparatus for displaying an image, including: an input image node configured to provide at least a first and a second image modulated lights; and a holographic waveguide device configured to propagate the at least one of the first and second image modulated lights in at least a first direction. The holographic waveguide device includes: at least a first and second interspersed multiplicities of grating elements disposed in at least one layer, the first and second grating elements having respectively a first and a second prescriptions. The first and second multiplicity of grating elements are configured to deflect respectively the first and second image modulated lights out of the at least one layer into respectively a first and a second multiplicities of output rays forming respectively a first and second FOV tiles.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/849,043, filed Apr. 15, 2020, which is a continuation of U.S. patentapplication Ser. No. 15/048,954, now U.S. Pat. No. 10,690,915, filedFeb. 19, 2016, which is a continuation of U.S. patent application Ser.No. 13/869,866, now U.S. Pat. No. 9,341,846, filed Apr. 24, 2013, whichclaims the benefit of and priority to U.S. Application No. 61/687,436,filed Apr. 25, 2012, and 61/689,907, filed Jun. 15, 2012, each of whichis hereby incorporated by reference herein in their entirety.

BACKGROUND

There is a need for a compact see through data display capable ofdisplaying image content ranging from symbols and alphanumeric arrays tohigh-resolution pixelated images. The display should be highlytransparent and the displayed image content should be clearly visiblewhen superimposed over a bright background scene. The display shouldprovide full color with an enhanced color gamut for optimal datavisibility and impact. A desirable feature is that the display should beas easy to wear, natural and non-distracting as possible with a formfactor similar to that of ski goggles or, more desirably, sunglasses.The eye relief and pupil should be big enough to avoid image loss duringhead movement even for demanding military and sports activities. Theimage generator should be compact, solid state and have low powerconsumption.

The above goals are not achieved by current technology. Current wearabledisplays only manage to deliver see through, adequate pupils, eye reliefand field of view and high brightness simultaneously at the expense ofcumbersome form factors. In many cases weight is distributed inundesirable place for a wearable display in front of the eye. One commonapproach to providing see through relies on reflective or diffractivevisors illuminated off axis. Microdisplays, which providehigh-resolution image generators in tiny flat panels, often do notnecessarily help with miniaturizing wearable displays because a generalneed for very high magnifications inevitably results in large diameteroptics. Several ultra low form factor designs offering spectacle-likeform factors are currently available but usually demand aggressivetrade-offs against field of view (FOV), eye relief and exit pupil.

A long-term goal for research and development in HMDs is to createnear-to-eye, color HMDs featuring:

-   -   a) high resolution digital imagery exceeding the angular        resolution of standard NVGs over the entire field of view and        focused at infinity;    -   b) a 80°×40° monocular field-of-view (FOV) HMD, or a 120°×40°        binocular FOV HMD with 40° stereoscopic overlap at the center of        the FOV;    -   c) a high see-through (≥90%) display with an unobstructed        panoramic view of the outside world, a generous eye box, and        adequate eye relief; and    -   d) a light-weight, low-profile design that integrates well with        both step-in visors and standard sand, wind and dust goggles.

Although the imagery will be displayed over a certain field of view, thepanoramic see-through capability may be much greater than this andgenerally better than the host visor or goggles. This is an improvementover existing NVGs, where the surrounding environment is occludedoutside the 40° field of view.

One desirable head-worn display is one that: (1) preserves situationalawareness by offering a panoramic see-through with high transparency;and (2) provides high-resolution, wide-field-of-view imagery. Such asystem should also be unobtrusive; that is, compact, light-weight, andcomfortable, where comfort comes from having a generous exit pupil andeye motion box/exit pupil (>15 mm), adequate eye relief (≥25 mm),ergonomic center of mass, focus at infinity, and compatibility withprotective head gear. Current and future conventional refractive opticscannot satisfy this suite of requirements. Other importantdiscriminators include: full color capability, field of view, pixelresolution, see-through, luminance, dynamic grayscale and low powerconsumption. Even after years of highly competitive development, HWDsbased on refractive optics exhibit limited field of view and are notcompact, light-weight, or comfortable.

Head-mounted displays based on waveguide technology substrate guideddisplays have demonstrated the capability of meeting many of these basicrequirements. Of particular relevance is a patent (U.S. Pat. No.5,856,842) awarded to Kaiser Optical Systems Inc. (KOSI), a RockwellCollins subsidiary, in 1999, which teaches how light can be coupled intoa waveguide by employing a diffractive element at the input and coupledout of the same waveguide by employing a second diffractive element atthe output. According to U.S. Pat. No. 5,856,842, the light incident onthe waveguide needs to be collimated in order to maintain its imagecontent as it propagates along the waveguide. That is, the light shouldbe collimated before it enters the waveguide. This can be accomplishedby many suitable techniques. With this design approach, light leavingthe waveguide may be naturally collimated, which is the condition neededto make the imagery appear focused at infinity. Light propagates along awaveguide only over a limited range of internal angles. Lightpropagating parallel to the surface will (by definition) travel alongthe waveguide without bouncing. Light not propagating parallel to thesurface will travel along the waveguide bouncing back and forth betweenthe surfaces, provided the angle of incidence with respect to thesurface normal is greater than some critical angle. For BK-7 glass, thiscritical angle is ˜42°. This can be lowered slightly by using areflective coating (but this may diminish the see through performance ofthe substrate) or by using a higher-index material. Regardless, therange of internal angles over which light will propagate along thewaveguide does not vary significantly. Thus, for glass, the maximumrange of internal angles is ≤50°. This translates into a range of anglesexiting the waveguide (i.e.; angles in air) of <40°; generally less,when other design factors are taken into account.

To date, SGO technology has not gained wide-spread acceptance. This maybe due to the fact that waveguide optics can be used to expand the exitpupil but they cannot be used to expand the field of view or improve thedigital resolution. That is, the underlying physics, which constraintsthe range of internal angles that can undergo total internal reflection(TIR) within the waveguide, may limit the achievable field of view withwaveguide optics to at most 40° and the achievable digital resolution tothat of the associated image.

BRIEF SUMMARY OF INVENTION

In view of the foregoing, the Inventors have recognized and appreciatedthe advantages of a display and more particularly to a transparentdisplay that combines Substrate Guided Optics (SGO) and Switchable BraggGratings (SBGs).

Accordingly, provided in one aspect of some embodiments is an apparatusfor displaying an image, comprising: an input image node configured toprovide at least a first and a second image modulated lights; and aholographic waveguide device configured to propagate the at least one ofthe first and second image modulated lights in at least a firstdirection. The holographic waveguide device may comprise: at least afirst and second interspersed multiplicities of grating elementsdisposed in at least one layer, the first and second grating elementshaving respectively a first and a second prescriptions. The first andsecond image modulated lights may be modulated respectively with firstfield of view (FOV) and second FOV image information. The firstmultiplicity of grating elements may be configured to deflect the firstimage modulated light out of the at least one layer into a firstmultiplicity of output rays forming a first FOV tile, and the secondmultiplicity of grating elements may be configured to deflect the secondimage modulated light out of the layer into a second multiplicity ofoutput rays forming a second FOV tile.

Provided in another aspect of some embodiments is a method of displayingan image, the method comprising: (i) providing an apparatus comprising:an input image node and a holographic waveguide device comprising (M×N)interspersed multiplicities of grating elements, where M, N areintegers; (ii) generating image modulated light (I,J) input image nodecorresponding to field of view (FOV) tile (I,J), for integers 1≤I≤N and1≤J≤M; (iii) switching grating elements of prescription matching FOVtile (I,J) to their diffracting states; (iv) illuminating gratingelements of prescription matching FOV tile (I,J) with image modulatedlight (I,J); and (v) diffracting the image modulated light I, J into FOVtile I, J.

A more complete understanding of the invention can be obtained byconsidering the following detailed description in conjunction with theaccompanying drawings, wherein like index numerals indicate like parts.For purposes of clarity, details relating to technical material that isknown in the technical fields related to the invention have not beendescribed in detail.

It should be appreciated that all combinations of the foregoing conceptsand additional concepts discussed in greater detail below (provided suchconcepts are not mutually inconsistent) are contemplated as being partof the inventive subject matter disclosed herein. In particular, allcombinations of claimed subject matter appearing at the end of thisdisclosure are contemplated as being part of the inventive subjectmatter disclosed herein. It should also be appreciated that terminologyexplicitly employed herein that also may appear in any disclosureincorporated by reference should be accorded a meaning most consistentwith the particular concepts disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The skilled artisan will understand that the drawings primarily are forillustrative purposes and are not intended to limit the scope of theinventive subject matter described herein. The drawings are notnecessarily to scale; in some instances, various aspects of theinventive subject matter disclosed herein may be shown exaggerated orenlarged in the drawings to facilitate an understanding of differentfeatures. In the drawings, like reference characters generally refer tolike features (e.g., functionally similar and/or structurally similarelements).

FIG. 1 is a schematic illustration of a color waveguide displayarchitecture using stacked gratings where each grating prescriptioncorresponds to waveguide light being diffracted into a unique field ofview tile.

FIG. 2 is a schematic cross section view of a waveguide display in oneembodiment using stacked gratings indicating the FOV provided by eachgrating.

FIG. 3A is a schematic cross section view of a tessellated waveguidedisplay in one embodiment showing a detail of the tessellation pattern.

FIG. 3B is a schematic cross section view of a tessellated waveguidedisplay in one embodiment showing a detail of the tessellation patternin which the grating elements are uniformly interspersed.

FIG. 3C is a schematic cross section view of a tessellated waveguidedisplay in one embodiment showing a detail of the tessellation patternin which the grating elements are randomly interspersed.

FIG. 4 is a schematic front elevation view of the function elements of atessellated waveguide display in one embodiment.

FIG. 5 is a schematic front elevation view of a tessellated waveguidedisplay in one operational state in one embodiment.

FIG. 6 is a schematic front elevation view of a tessellated waveguidedisplay showing details of the Input Image Node in one embodiment.

FIG. 7 illustrates the operation of the Input Image Node in oneembodiment.

FIG. 8A is a tessellation pattern comprising rectangular elements ofdiffering size and aspect ratio in one embodiment.

FIG. 8B is a tessellation pattern comprising Penrose tiles in oneembodiment.

FIG. 8C is a tessellation pattern comprising hexagons in one embodiment.

FIG. 8D is a tessellation pattern comprising squares in one embodiment.

FIG. 9A is a tessellation pattern comprising diamond-shaped elements inone embodiment.

FIG. 9B is a tessellation pattern comprising isosceles triangles in oneembodiment.

FIG. 10A is a tessellation pattern comprising hexagons of horizontallybiased aspect ratio in one embodiment.

FIG. 10B is a tessellation pattern comprising rectangles of horizontallybiased aspect ratio in one embodiment.

FIG. 10C is a tessellation pattern comprising diamond shaped elements ofhorizontally biased aspect ratio in one embodiment.

FIG. 10D is a tessellation pattern comprising triangles of horizontallybiased aspect ratio in one embodiment.

FIG. 11 is a schematic cross sectional view of a tessellated waveguidecontaining two grating layers in one embodiment.

FIG. 12A shows an example of a tessellation pattern comprising fourdifferent grating element types with an eye pupil overlaid in oneembodiment.

FIG. 12B shows an example of a tessellation pattern comprising onegrating element types with an eye pupil overlaid in one embodiment.

FIG. 12C shows an example of a tessellation pattern comprising twodifferent grating element types with an eye pupil overlaid in oneembodiment.

FIG. 12D shows an example of a tessellation pattern comprising threedifferent grating element types with an eye pupil overlaid in oneembodiment.

FIG. 13 shows an example of a tessellation pattern for one particulargrating element type with an eye pupil overlaid in one embodiment.

FIG. 14 is a chart showing the MTF versus angular frequency for thetessellation pattern of FIG. 13 in one embodiment.

FIG. 15 shows an example of a tessellation pattern using rectangularelements of horizontally biased aspect ratio and comprising elements offive different types in one embodiment.

FIG. 16A illustrates the projection into the exit pupil of tessellationelements of a first type corresponding to a first field of view with aneye pupil overlaid in one embodiment.

FIG. 16B illustrates the projection into the exit pupil of tessellationelements of a second type corresponding to a second field of view withan eye pupil overlaid in one embodiment.

FIG. 16C illustrates the projection into the exit pupil of tessellationelements of a third type corresponding to a third field of view with aneye pupil overlaid in one embodiment.

FIG. 16D shows the field of view tile corresponding to the tessellationelements of FIG. 16A in one embodiment.

FIG. 16E shows the field of view tile corresponding to the tessellationelements of FIG. 16B.

FIG. 16F shows the field of view tile corresponding to the tessellationelements of FIG. 16C in one embodiment.

FIG. 17 shows the distribution of tessellation element types withinregions labelled by numerals 1-7 used to provide a field of view tilingpattern illustrated in FIG. 18 in one embodiment.

FIG. 18 shows a field of view tiling pattern comprising four horizontaltiles and three vertical tiles.

FIG. 19A shows a tessellation pattern comprising elements of one typefrom regions 1 and 7 in one layer of a two layer waveguide in theembodiment illustrated in FIGS. 17-18 in one embodiment.

FIG. 19B shows overlaid tessellation patterns from both layers of thewaveguide of FIG. 19A in one embodiment.

FIG. 20A shows a tessellation pattern comprising elements of one typefrom regions 2 and 6 in one layer of a two layer waveguide in theembodiment illustrated in FIGS. 17-18 in one embodiment.

FIG. 20B shows overlaid tessellation patterns from both layers of thewaveguide of FIG. 20A in one embodiment.

FIG. 21A shows a tessellation pattern comprising elements of one typefrom regions 3 and 5 in one layer of a two layer waveguide in theembodiment of the invention illustrated in FIGS. 17-18 in oneembodiment.

FIG. 21B shows overlaid tessellation patterns from both layers of thewaveguide of FIG. 21A in one embodiment.

FIG. 22A shows a tessellation pattern comprising elements of one typefrom region 4 in one layer of a two layer waveguide in the embodiment ofthe invention illustrated in FIGS. 17-18.

FIG. 22B shows overlaid tessellation patterns from both layers of thewaveguide of FIG. 22A in one embodiment.

FIG. 23 illustrates the composite tessellation pattern resulting fromthe superposition of the tiling patterns of FIGS. 19A-22B in oneembodiment.

FIG. 24 shows an example of a tessellation pattern in a two layerwaveguide for grating elements of one type only in one embodiment.

FIG. 25 shows the composite tessellation pattern in a first layer of atwo layer waveguide in one embodiment.

FIG. 26 shows the composite tessellation pattern in a second layer of atwo layer waveguide in one embodiment.

FIG. 27A is a schematic cross section view showing the image outputportion of an Input Image Node in one embodiment.

FIG. 27B is a schematic cross section view showing the image inputportion of an Input Image Node in one embodiment.

FIG. 28A is a cross section view showing the Input Image Node and itscoupling to the DigiLens waveguide via the Vertical Beam Expander in oneembodiment.

FIG. 28B shows a ray trace of the embodiment of FIG. 28A in oneembodiment.

FIG. 29 is a plan view of the DigiLens waveguide and the Vertical BeamExpander in one embodiment.

FIG. 30A shows a waveguide 252 with input rays directed into the TIRpaths by a coupling grating in one embodiment.

FIG. 30B shows a waveguide in one embodiment having input couplingoptics comprising the first and second gratings disposed adjacent eachother, the half wave film sandwiched by the waveguide and the firstgrating; and a polarizing beam splitter (PBS) film sandwiched by thewaveguide and the second.

FIG. 31 is a schematic cross section of a portion of a waveguide used inthe invention in which light is extracted from the waveguide in opposingdirections in one embodiment.

FIG. 32 is a schematic cross section of a portion of a waveguide used inthe invention incorporating a beam splitter layer for improvingillumination uniformity in one embodiment.

FIG. 33 illustrates a method of reducing the number of wiring tracks inan electrode layer using dual sided addressing in one embodiment.

FIG. 34 illustrates one scheme for interleaving electrode wiring tracksin a tessellated waveguide in one embodiment.

FIG. 35 illustrates another scheme for interleaving electrode wiringtracks in a tessellated waveguide in one embodiment.

FIG. 36 illustrates a further scheme for interleaving electrode wiringtracks in a tessellated waveguide in one embodiment.

FIG. 37A shows a schematic plan view of a curved visor implementation ofthe invention in one embodiment.

FIG. 37B shows a schematic side elevation view of a curved visorimplementation of the invention in one embodiment.

FIG. 38 show a cross section of a curved visor implementation of theinvention in which the DigiLens comprises laminated optically isolatedwaveguides in one embodiment.

FIG. 39 show a cross section of a curved visor implementation of theinvention in which the DigiLens comprises laminated grating layers thatform a single waveguiding structure in one embodiment.

FIG. 40A shows a cross section of a curved visor implementation of theinvention in which the DigiLens comprises facetted elements in oneembodiment.

FIG. 40B shows the optical interface between two of the facettedelements of FIG. 40A in one embodiment.

FIG. 40C illustrates the optical interface between two of the facettedelements of FIG. 40A in more detail in one embodiment.

FIG. 41 show a cross section of a curved visor implementation of theinvention in which the DigiLens comprises facetted elements embedded ina curved lightguide in one embodiment.

FIG. 42A is a chart showing the variation of diffraction efficiency withangle for a micro tessellated pattern in one embodiment of the inventionin one embodiment.

FIG. 42B shows the micro-tessellation distribution corresponding to thechart of FIG. 42A in one embodiment.

FIG. 43A is a chart showing a MTF plot for a regular micro tessellationpattern with 50% aperture fill in one embodiment.

FIG. 43B is a schematic illustration showing the effect of 50% aperturefill produced by the micro tessellation pattern of FIG. 43A in oneembodiment.

FIG. 44A is a chart showing a MTF plot for a regular micro tessellationpattern with 25% aperture fill in one embodiment.

FIG. 44B is a schematic illustration showing the effect of 25% aperturefill produced by the micro tessellation pattern of FIG. 43A in oneembodiment.

FIG. 45A is a chart showing a MTF plot for a regular micro tessellationpattern with 50% aperture fill in one embodiment.

FIG. 45B is a footprint diagram for the case of FIG. 45A in oneembodiment.

FIG. 46A is a footprint diagram showing the effect of 75% aperture fillfor 50 micron micro tessellations in one embodiment.

FIG. 46B is a chart showing a MTF plot illustrating the effect of 75%aperture fill for 50 micron micro tessellations in one embodiment.

FIG. 47A is a footprint diagram showing the effect of 50% aperture fillfor 50 micron micro tessellations in one embodiment.

FIG. 47B is a chart showing a MTF plot illustrating the effect of 50%aperture fill for 50 micron micro tessellations in one embodiment.

FIG. 48A is a footprint diagram showing the effect of 25% aperture fillfor 50 micron micro tessellations in one embodiment.

FIG. 48B is a chart showing a MTF plot illustrating the effect of 25%aperture fill for 50 micron micro tessellations in one embodiment.

FIG. 49A is a footprint diagram showing the effect of 75% aperture fillfor 125 micron micro tessellations in one embodiment.

FIG. 49B is a chart showing a MTF plot illustrating the effect of 75%aperture fill for 125 micron micro tessellations in one embodiment.

FIG. 50A is a footprint diagram showing the effect of 50% aperture fillfor 125 micron micro tessellations in one embodiment.

FIG. 50B is a chart showing a MTF plot illustrating the effect of 50%aperture fill for 125 micron micro tessellations in one embodiment.

FIG. 51A is a footprint diagram showing the effect of 25% aperture fillfor 125 micron micro tessellations in one embodiment.

FIG. 51B is a chart showing a MTF plot illustrating the effect of 25%aperture fill for 125 micron micro tessellations in one embodiment.

FIG. 52A is a footprint diagram showing the effect of 75% aperture fillfor 250 micron micro tessellations in one embodiment.

FIG. 52B is a chart showing a MTF plot illustrating the effect of 75%aperture fill for 250 micron micro tessellations in one embodiment.

FIG. 53A is a footprint diagram showing the effect of 50% aperture fillfor 250 micron micro tessellations in one embodiment.

FIG. 53B is a chart showing a MTF plot illustrating the effect of 50%aperture fill for 250 micron micro tessellations in one embodiment.

FIG. 54A is a footprint diagram showing the effect of 25% aperture fillfor 250 micron micro tessellations in one embodiment.

FIG. 54B is a chart showing a MTF plot illustrating the effect of 25%aperture fill for 250 micron micro tessellations in one embodiment.

FIG. 55A is a footprint diagram showing the effect of 1 mm tessellationat 50% aperture fill for 125 micron micro tessellations for a 3 mm eyepupil diameter in one embodiment.

FIG. 55B is a chart showing a MTF plot illustrating the effect of 1 mmtessellation at 50% aperture fill for 125 micron micro tessellations fora 3 mm eye pupil diameter in one embodiment.

FIG. 56A is a footprint diagram showing the effect of 1.5 mmtessellation at 50% aperture fill for 125 micron micro tessellations fora 3 mm eye pupil diameter in one embodiment.

FIG. 56B is a chart showing a MTF plot illustrating the effect of 1.5 mmtessellation at 50% aperture fill for 125 micron micro tessellations fora 3 mm eye pupil diameter in one embodiment.

FIG. 57A is a footprint diagram showing the effect of 3 mm tessellationat 50% aperture fill for 125 micron micro tessellations for a 3 mm eyepupil diameter in one embodiment.

FIG. 57B is a chart showing a MTF plot illustrating the effect of 3 mmtessellation at 50% aperture fill for 125 micron micro tessellations fora 3 mm eye pupil diameter in one embodiment.

FIG. 58A is a chart showing the MTF of a User Defined Aperture in oneembodiment.

FIG. 58B is a chart showing the MTF of a Bitmap Aperture Function in oneembodiment.

FIG. 59A is a Bitmap Aperture Function in one embodiment of theinvention in one embodiment.

FIG. 59B is a chart showing diffraction efficiency versus angle for theembodiment of FIG. 59A in one embodiment.

FIG. 60 is a MTF plot showing the effect of 1.0 mm tessellation using125 um micro tessellations randomly positioned with variabletransmission and a 3 mm eye pupil in one embodiment.

FIG. 61 is a Bitmap Aperture Function in one embodiment.

FIG. 62 is a MTF plot showing the effect of 1.5 mm tessellation using125 um micro tessellations randomly positioned with variabletransmission and a 3 mm eye pupil in one embodiment.

FIG. 63 is a first illumination uniformity analysis of a firstimplementation tessellation pattern in one embodiment.

FIG. 64 is a second illumination uniformity analysis of a firstimplementation tessellation pattern in one embodiment.

FIG. 65 is a third illumination uniformity analysis of a firstimplementation tessellation pattern in one embodiment.

FIG. 66 is a fourth illumination uniformity analysis of a firstimplementation tessellation pattern in one embodiment.

FIG. 67 is a fifth illumination uniformity analysis of a firstimplementation tessellation pattern in one embodiment.

FIG. 68 is a sixth illumination uniformity analysis of a firstimplementation tessellation pattern in one embodiment.

FIG. 69 is a seventh illumination uniformity analysis of a firstimplementation tessellation pattern in one embodiment.

FIG. 70 is an eighth illumination uniformity analysis of a firstimplementation tessellation pattern in one embodiment.

FIG. 71 is a ninth illumination uniformity analysis of a firstimplementation tessellation pattern in one embodiment.

FIG. 72 is a tenth illumination uniformity analysis of a firstimplementation tessellation pattern in one embodiment.

FIG. 73 is an eleventh illumination uniformity analysis of a firstimplementation tessellation pattern in one embodiment.

FIG. 74 is a twelfth illumination uniformity analysis of a firstimplementation tessellation pattern in one embodiment.

FIG. 75 is a thirteenth illumination uniformity analysis of a firstimplementation tessellation pattern in one embodiment in one embodiment.

DETAILED DESCRIPTION

Following below are more detailed descriptions of various conceptsrelated to, and embodiments of, an inventive display. It should beappreciated that various concepts introduced above and discussed ingreater detail below may be implemented in any of numerous ways, as thedisclosed concepts are not limited to any particular manner ofimplementation. Examples of specific implementations and applicationsare provided primarily for illustrative purposes.

Various Embodiments

Provided in one embodiment is an apparatus for displaying an image,comprising: an input image node configured to provide at least a firstand a second image modulated lights; and a holographic waveguide deviceconfigured to propagate the at least one of the first and second imagemodulated lights in at least a first direction. The holographicwaveguide device may comprise: at least a first and second interspersedmultiplicities of grating elements disposed in at least one layer, thefirst and second grating elements having respectively a first and asecond prescriptions. The first and second image modulated lights may bemodulated respectively with first field of view (FOV) and second FOVimage information. The first multiplicity of grating elements may beconfigured to deflect the first image modulated light out of the atleast one layer into a first multiplicity of output rays forming a firstFOV tile, and the second multiplicity of grating elements may beconfigured to deflect the second image modulated light out of the layerinto a second multiplicity of output rays forming a second FOV tile.

Provided in another embodiment is an apparatus for displaying an image,comprising: an input image node configured to provide at least a firstand a second image modulated lights; and a holographic waveguide deviceconfigured to propagate the at least one of the first and second imagemodulated lights in at least a first direction. The holographicwaveguide device may comprise: at least a first and second interspersedmultiplicities of grating elements disposed in at least one layer, thefirst and second grating elements having respectively a first and asecond prescriptions. The first and second image modulated lights may bemodulated respectively with first field of view (FOV) and second FOVimage information. The first multiplicity of grating elements may beconfigured to deflect the first image modulated light out of the atleast one layer into a first multiplicity of output rays forming a firstFOV tile, and the second multiplicity of grating elements may beconfigured to deflect the second image modulated light out of the layerinto a second multiplicity of output rays forming a second FOV tile. Thefirst and second multiplicities of the grating elements may comprise anSBG in a passive mode or a switching mode.

Provided in another embodiment is an apparatus for displaying an image,comprising: an input image node configured to provide at least a firstand a second image modulated lights; a beam expander; and a holographicwaveguide device configured to propagate the at least one of the firstand second image modulated lights in at least a first direction. Theholographic waveguide device may comprise: at least a first and secondinterspersed multiplicities of grating elements disposed in at least onelayer, the first and second grating elements having respectively a firstand a second prescriptions. The first and second image modulated lightsmay be modulated respectively with first field of view (FOV) and secondFOV image information. The first multiplicity of grating elements may beconfigured to deflect the first image modulated light out of the atleast one layer into a first multiplicity of output rays forming a firstFOV tile, and the second multiplicity of grating elements may beconfigured to deflect the second image modulated light out of the layerinto a second multiplicity of output rays forming a second FOV tile.

Provided in another embodiment is an apparatus for displaying an image,comprising: an input image node configured to provide at least a firstand a second image modulated lights; and a holographic waveguide deviceconfigured to propagate the at least one of the first and second imagemodulated lights in at least a first direction. The holographicwaveguide device may comprise: at least a first and second interspersedmultiplicities of grating elements disposed in at least one layer, thefirst and second grating elements having respectively a first and asecond prescriptions. The first and second image modulated lights may bemodulated respectively with first field of view (FOV) and second FOVimage information. The first multiplicity of grating elements may beconfigured to deflect the first image modulated light out of the atleast one layer into a first multiplicity of output rays forming a firstFOV tile, and the second multiplicity of grating elements may beconfigured to deflect the second image modulated light out of the layerinto a second multiplicity of output rays forming a second FOV tile. Atleast one of the first and second multiplicities of the grating elementsmay be tessellated in a predetermined pattern.

In one embodiment, at least one of the first and second multiplicitiesof the grating elements comprise an SBG that is in a switching mode orin a passive mode.

In one embodiment, at least one of the first and second multiplicitiesof the grating elements are electrically switchable.

In one embodiment, at least one of the first and second multiplicitiesof the grating elements have a non-diffracting state and a diffractingstate having a diffraction efficiency lying between a predeterminedminimum level and a maximum level.

In one embodiment, all elements in the first or second multiplicities ofgrating elements are configured to be switched.

In one embodiment, at least one of the first and second multiplicitiesof the grating elements have a diffracting state, and when in thediffracting state. The first grating elements are configured to deflectthe first image modulated light out of the at least one layer into thefirst multiplicity of output rays forming a first FOV tile. The secondgrating elements are configured to deflect the second image modulatedlight out of the layer into the second multiplicity of output raysforming a second FOV tile.

In one embodiment, the at least one layer is sandwiched betweentransparent substrates to which patterned electrodes are applied.

In one embodiment, the at least one layer is sandwiched betweentransparent substrates to which patterned electrodes are applied, and atleast one of the patterned electrodes comprises a first multiplicity ofelectrode elements overlapping the first multiplicity of the firstgrating elements and a second multiplicity of electrode elementsoverlapping the second multiplicity of the second grating elements.

In one embodiment, at least one of the first and second multiplicitiesof the grating elements have a diffraction efficiency that is spatiallydependent.

In one embodiment, at least one of the first and second multiplicitiesof the grating elements have a diffraction efficiency that increaseswith distance along a length of the waveguide.

In one embodiment, within the at least one layer the grating elementshave integer N1 different prescription interspersed in a first band,abutted to the left and right, in sequence, by bands containing elementsof integer N2 different prescriptions where N1>N2, N3 differentprescriptions where N2>N3, and integer N4 different prescriptions whereN3>N4. In one embodiment, at least one of the first and secondmultiplicities of grating elements have 12 different prescriptionsinterspersed in a first band, abutted to the left and right, insequence, by bands containing elements of 9 different prescriptions, 6different prescriptions, and 1 prescription.

In one embodiment, each the FOV tile is configured to provide an imageat infinity.

In one embodiment, each the FOV tile is configured to provide an imageat a far point of the human eye.

In one embodiment, the holographic waveguide device comprises at leastone of beam splitter lamina, a quarter wave plate, and a grating devicefor polarization recovery.

In one embodiment, the image modulated light from at least one gratingelement of a given prescription is present within an exit pupil regionbounded by the instantaneous aperture of the human eye pupil. In oneembodiment, the image modulate light from at least three gratingelements of a given prescription is present.

In one embodiment, the FOV tiles abut in FOV space to form a rectangularFOV.

In one embodiment, the FOV tiles abut in FOV space to provide acontinuous field of view.

In one embodiment, at least two the FOV tiles overlap.

In one embodiment, the FOV tiles abut to provide a FOV of approximately40 degrees horizontally by 30 degrees vertically.

In one embodiment, the FOV tiles abut to provide a FOV of approximately60 degrees horizontally by 30 degrees vertically.

In one embodiment, wherein the FOV tiles abut to provide a FOV ofapproximately 80 degrees horizontally by 80 degrees vertically.

In one embodiment, the input image node further comprises a despeckler.

In one embodiment, at least one of the first and second multiplicitiesof the grating elements are recorded in HPDLC.

In one embodiment, at least one of the first and second multiplicitiesof the grating elements are reverse mode SBGs.

In one embodiment, the holographic waveguide device is curved.

In one embodiment, at least one of the first and second multiplicitiesof grating elements have varying thickness.

In one embodiment, the holographic waveguide device comprises facetedsections abutting edge to edge.

In one embodiment, the holographic waveguide device comprises facetedsections abutting edge to edge and embedded in a plastic continuouslycurved volume.

In one embodiment, the holographic waveguide device comprises plastic.

In one embodiment, the holographic waveguide device is configured toprovide exit pupil expansion in the first direction, and the beamexpander is configured to provide exit pupil expansion in a seconddirection.

In one embodiment, the holographic waveguide device is configured toprovide exit pupil expansion in the first direction, and the beamexpander is configured to provide exit pupil expansion in a seconddirection that is orthogonal to the first direction.

In one embodiment, the beam expander further comprises: an input portfor image modulated light from the input image node; an output port; andat least one waveguide layer configured to propagate light in a seconddirection. The at least one waveguide layer may comprise at least onegrating lamina configured to extract the modulated light from asubstrate along the second direction into the first direction throughthe output port.

In one embodiment, the beam expander further comprises at least onewaveguide layer that comprises at least two grating lamina disposedadjacently.

In one embodiment, the beam expander further comprises at least onewaveguide layer that comprises at least two overlapping grating lamina.

In one embodiment, the beam expander incorporates at least one of a beamsplitter lamina, a quarter wave plate, and a grating device forpolarization recovery.

In one embodiment, the first and second image modulated lights arepresented sequentially.

In one embodiment, at least one of the first and second modulated imagelights undergoes total internal reflection (TIR) within the waveguidedevice.

In one embodiment, the input image node comprises at least one of amicrodisplay, a light source configured to illuminate the microdisplay,a processor for writing image data to the microdisplay, and acollimation lens, a relay lens, a beam splitter, and a magnificationlens.

In one embodiment, the first and second multiplicities of the gratingelements are tessellated in a predetermined pattern.

In one embodiment, the predetermined pattern is at least one of aperiodic pattern, a non-periodic pattern, a self-similar pattern, anon-self-similar tiling pattern, and randomly distributed pattern. Inone embodiment, a non-periodic pattern may be a Penrose tiling pattern.In another embodiment, a self-similar pattern may be a Penrose tilingpattern.

In one embodiment, all elements in the first or second multiplicities ofgrating elements are configured to be switched into a diffracting statesimultaneously.

In one embodiment, at least one of the first and second multiplicitiesof the grating elements have at least one axis of symmetry.

In one embodiment, at least one of the first and second multiplicitiesof the grating elements have a shape that comprises at least one of asquare, triangle and diamond.

In one embodiment, elements of the first multiplicity of gratingelements have a first geometry and elements of the second multiplicityof grating elements have a second geometry.

In one embodiment, at least one of the first and second grating elementshave at least two different geometries.

In one embodiment, all grating elements in the at least one the layerare optimized for one wavelength.

In one embodiment, at least one of the first and second grating elementsin the at least one layer are optimised for at least two wavelengths.

In one embodiment, at least one of the first and second grating elementshave multiplexed prescriptions optimized for at least two differentwavelengths.

In one embodiment, at least one of the first and second grating elementshave multiplexed prescriptions optimized for at least two differentdiffraction efficiency angular bandwidths.

In one embodiment, at least one of the first and second image modulatedlights is collimated.

In one embodiment, at least one of the first and second image modulatedlights is polarized.

In one embodiment, the apparatus may further comprise an illuminationsource comprising a laser providing light of at least one wavelength.

In one embodiment, the holographic waveguide device is configured toprovide a transparent display.

Provided in some embodiments are devices comprising the apparatus asdescribed herein. The device may be a part of a reflective display. Thedevice may be a part of a stereoscopic display in which the first andsecond image modulated light provides left and right eye perspectiveviews. The device may be a part of a real image forming display. Thedevice may be a part of at least one of HMD, HUD, and HDD. The devicemay be a part of a contact lens.

In one embodiment, the input image node comprises at least one of amicrodisplay, a light source configured to illuminate the microdisplay,a processor for writing image data to the microdisplay, and acollimation lens, a relay lens, a beam splitter and a magnificationlens.

Provided in another embodiment is a method of displaying an image, themethod comprising: (i) providing an apparatus comprising: an input imagenode and a holographic waveguide device comprising (M×N) interspersedmultiplicities of grating elements, where M, N are integers; (ii)generating image modulated light (I,J) input image node corresponding tofield of view (FOV) tile (I,J), for integers 1≤I≤N and 1≤J≤M; (iii)switching grating elements of prescription matching FOV tile (I,J) totheir diffracting states; (iv) illuminating grating elements ofprescription matching FOV tile (I,J) with image modulated light (I,J);and (v) diffracting the image modulated light I, J into FOV tile I, J.

In one embodiment, the method may further comprise repeating (ii)-(v)until achieving full FOV tiled.

In one embodiment, the method may further comprise sampling the inputimage into a plurality of angular intervals, each of the plurality ofangular intervals having an effective exit pupil that is a fraction ofthe size of the full pupil.

In one embodiment, the method may further comprise improving thedisplaying of the image by modifying at least one of the following ofthe at least one grating lamina of at least one of the first and secondoptical substrates: grating thickness, refractive index modulation,k-vector, surface grating period, and hologram-substrate indexdifference.

It should be appreciated that all combinations of the foregoing conceptsand additional concepts discussed in greater detail below (provided suchconcepts are not mutually inconsistent) are contemplated as being partof the inventive subject matter disclosed herein. In particular, allcombinations of claimed subject matter appearing at the end of thisdisclosure are contemplated as being part of the inventive subjectmatter disclosed herein. It should also be appreciated that terminologyexplicitly employed herein that also may appear in any disclosureincorporated by reference should be accorded a meaning most consistentwith the particular concepts disclosed herein.

At least some embodiments provided herein overcome the challenges oftiling large FOVs using a multiplicity of different gratingprescriptions in a waveguide HMD of the type disclosed in U.S. Pat. No.8,233,204. In one embodiment, grating angular bandwidth constraintscould limit the size of FOV tiles to around 10°×10° leading tounmanageably large grating stacks as the number of vertical andhorizontal FOV tiles increased. Attempting full color would increase thenumber of layers by a factor of 3.

One important feature of the embodiments described herein is thatinstead of stacking gratings of different prescriptions, they arechopped up into small elements which are then interspersed intotessellation patterns in one or more overlapping layers.

One embodiment of a tessellated display may comprise an Input Image Node(IIN); a first beam expander waveguide (usually vertical); and a secondbeam expander waveguide (usually horizontal) which also serves as aneyepiece. In one embodiment, the eyepiece combines the tessellation andbeam expansion functions. Each waveguide may contain input and outputBragg gratings. Each of the waveguides may comprise more than onegrating layer. In color embodiments, a separate monochromatic waveguidemay be used for each primary color. Another option for providing coloris to record multiplexed gratings, in which holograms with differentcolor prescriptions are superimposed, into a waveguide. Multiplexing mayalso be used to combine gratings of different angular bandwidth.

Many different tessellation schemes are possible including periodic(i.e., invariant under lateral displacement), non-periodic, self similarand random schemes. The patterns may be designed to provide more detailin near the centre FOV. Embodiments provided herein encompass passive orswitchable tessellation solutions and include hybrid solutions thatcombine passive and switchable elements.

In one embodiment, rays diffracted from each tessellation element form afootprint in the exit pupil. Typically, there must be at least two suchfootprints within an instantaneous eye pupil area. The precise numberwill depend on factors such as tessellation size and shape. In oneembodiment, tessellation may present significant design and fabricationchallenges. The tiny (few millimetre) grating elements result inresolution loss and illumination ripple, both of which have proveddifficult to correct. The holographic recording and electrode patterningof tessellated holographic arrays may be difficult with currentprocesses. These challenges may be overcome by using the passive gratingelements. In one embodiment, bandwidth may be increased in thetangential plane by making gratings thinner, while broad bandwidth inthe orthogonal, sagittal, plane may be achieved. Tessellation may offera route to larger FOVs if the above design and fabrications problems canbe solved. A FOV of 80°×80° in color is a reasonable goal.

One embodiment uses separate vertical and horizontal beam expansionwaveguides to provide an enlarged exit pupil (or eye box). In oneembodiment, collimated image light from the IIN is fed into the firstbeam expansion waveguide with a FOV defined by the microdisplay andcollimating optics. One embodiment allows the input or “coupling” opticsto be configured in many different ways ranging from classical opticallens-mirror designs to more compact designs based entirely ondiffractive (holographic) optics. One embodiment may be implementedusing all-passive gratings (although the use of switchable gratings ispreferred for large FOVs). Conventional passive gratings would not work.One benefit of using passive SBGs is that the refractive indexmodulation of the grating can be tuned from very low to very high valueswith a correspondingly broad range of diffraction efficiencies. The highindex modulation of SBGs results from the alternating bands ofpolymer-rich and LC-rich regions that form the Bragg fringes.Alternatively, active gratings may also be used, wherein the activegratings may be tuned from very low to very high values with acorrespondingly broad range of diffraction efficiencies.

The vertical and horizontal beam expanders may be based on lossywaveguides; that is, ones designed to extract light out of the waveguideuniformly along its length. As demonstrated in U.S. application Ser. No.13/844,456, filed Mar. 15, 2013, this may be achieved by varying thethickness (and modulation) across the grating. In one embodiment, in itssimplest case this entails creating a wedged grating (by inclining thecell walls) such that the hologram thickness increases in the directionof propagation. Generally, the grating thickness may vary from 1.0-1.2microns up to 2.8-3.0 microns, the lower thickness producing the lowestefficiency (and largest angular bandwidth). Some embodiments may allowmore sophisticated control of extraction by varying the thickness inorthogonal directions, using two wedge angles, or in a more generalfashion by applying curvature to one or both faces of the grating.

In one embodiment, beam expansion gratings are very thin (well below 3microns), which results in very broad diffraction efficiency angularbandwidth which, in turn. By optimising thickness and refractive indexmodulation it is possible to meet all of the desired gratingcharacteristics needed in the display—e.g., very high efficiency forcoupling into gratings and large dynamic range for the efficient,uniform extraction needed for beam expansion.

Image sampling can be used to enhance image transfer efficiency and formfactor. Coupling wide FOV image light into a waveguide would normallyresult in some loss of image angular content owing to the limited rangeof angles that can be efficiently propagated down a waveguide. Some ofthis light may couple out of the waveguide. At least some embodimentsdescribed herein may overcome this challenge by sampling the input imageinto multiple angular intervals, each of which has an effective exitpupil that is a fraction of the size of the full pupil, the thickness ofthe waveguide being reduced correspondingly.

One feature of the embodiments provided herein is the possibility ofcombining fixed frequency surface gratings at the input and output ofeach waveguide with rolled k-vectors. The surface grating may beintersection of the Bragg fringes with the substrate edge and accounts(approximately) for the basic ray optics of the waveguide. The k-vectoris the direction normal to the Bragg grating and accounts for thediffraction efficiency vs. angle characteristics of the grating. Byvarying the k-vector direction along the waveguide propagation direction(k-vector rolling), it is possible to, firstly, provide efficientcoupling of image light into the waveguide and, secondly, ensure thatonce coupled-in, all of the desired angular content is transmitted downthe waveguide with high efficiency. The k-vector rolling would desirablybe augmented by grating thickness control as discussed above.

In general the propagation of angular content down the waveguides can beoptimized by fine tuning of one or more of the following: gratingthickness; refractive index modulation; k-vector rolling; surfacegrating period; and the hologram-substrate index difference. Thetessellation pattern may include infrared sensitive elements forimplementing a waveguide eye tracker.

SBG Device

One way to create a much larger field of view is to parse it into a setof smaller fields of view (each compatible with the optical limitationsof the waveguide) and to (time) sequentially display them rapidly enoughthat the eye perceives them as a unified wide-angle display. One way todo this is by using holographic elements that can be sequentiallyswitched on and off very rapidly. One desirable solution to providingsuch switchable holographic elements is a device knows as a SwitchableBragg Grating (SBG).

The optical design benefits of diffractive optical elements (DOEs)include unique and efficient form factors and the ability to encodecomplex optical functions such as optical power and diffusion into thinlayers. Bragg gratings (also commonly termed volume phase gratings orholograms), which offer high diffraction efficiencies, have been widelyused in devices such as Head Up Displays. An important class of Bragggrating devices is known as a Switchable Bragg Grating (SBG). SBG is adiffractive device formed by recording a volume phase grating, orhologram, in a polymer dispersed liquid crystal (PDLC) mixture.Typically, SBG devices are fabricated by first placing a thin film of amixture of photopolymerizable monomers and liquid crystal materialbetween parallel glass plates or substrates. One or both glasssubstrates support electrodes, including for example transparent indiumtin oxide films, for applying an electric field across the PDLC layer. Avolume phase grating is then recorded by illuminating the liquidmaterial with two mutually coherent laser beams, which interfere to formthe desired grating structure. During the recording process, themonomers polymerize and the HPDLC mixture undergoes a phase separation,creating regions densely populated by liquid crystal micro-droplets,interspersed with regions of clear polymer. The alternating liquidcrystal-rich and liquid crystal-depleted regions form the fringe planesof the grating. The resulting volume phase grating can exhibit very highdiffraction efficiency, which may be controlled by the magnitude of theelectric field applied across the PDLC layer. When an electric field isapplied to the hologram via transparent electrodes, the naturalorientation of the LC droplets is changed causing the refractive indexmodulation of the fringes to reduce and the hologram diffractionefficiency to drop to very low levels. Note that the diffractionefficiency of the device can be adjusted, by, for example, the appliedvoltage over a continuous range from near 100% efficiency with novoltage applied to essentially zero efficiency with a sufficiently highvoltage applied.

SBGs may be used to provide transmission or reflection gratings for freespace applications. SBGs may be implemented as waveguide devices inwhich the HPDLC forms either the waveguide core or an evanescentlycoupled layer in proximity to the waveguide. In one particularconfiguration to be referred to here as Substrate Guided Optics (SGO)the parallel glass plates used to form the HPDLC cell provide a totalinternal reflection (TIR) light guiding structure. Light is “coupled”out of the SBG when the switchable grating diffracts the light at anangle beyond the TIR condition. SGOs are currently of interest in arange of display and sensor applications. Although much of the earlierwork on HPDLC has been directed at reflection holograms transmissiondevices are proving to be much more versatile as optical system buildingblocks.

The HPDLC used in SBGs may comprise liquid crystal (LC), monomers,photoinitiator dyes, and coinitiators. The mixture may include asurfactant. The patent and scientific literature contains many examplesof material systems and processes that may be used to fabricate SBGs.Two fundamental patents are: U.S. Pat. No. 5,942,157 by Sutherland, andU.S. Pat. No. 5,751,452 by Tanaka et al. both filings describe monomerand liquid crystal material combinations suitable for fabricating SBGdevices.

One of the known attributes of transmission SBGs is that the LCmolecules tend to align normal to the grating fringe planes. The effectof the LC molecule alignment is that transmission SBGs efficientlydiffract P polarized light (i.e., light with the polarization vector inthe plane of incidence) but have nearly zero diffraction efficiency forS polarized light (i.e., light with the polarization vector normal tothe plane of incidence. A glass light guide in air will propagate lightby total internal reflection if the internal incidence angle is greaterthan about 42 degrees. Thus, typically the embodiments usingtransmission SBGs described herein will use SBGs design to diffractinput P-polarized light entering the waveguide into TIR angles of about42 to about 70 degrees, or diffract TIR light at said angles into outputlight paths.

Normally SBGs diffract when no voltage is applied and are switching intotheir optically passive state when a voltage is application other times.However SBGs can be designed to operate in reverse mode such that theydiffract when a voltage is applied and remain optically passive at allother times. Methods for fabricating reverse mode SBGs may be anysuitable methods, such as for example those disclosed inPCT/GB2012/000680 by Popovich et al. The same reference also discloseshow SBGs may be fabricated using flexible plastic substrates to providethe benefits of improved ruggedness, reduce weight and safety in neareye applications.

The invention will now be further described by way of example only withreference to the accompanying drawings. It will be apparent to thoseskilled in the art that the present invention may be practiced with someor all of the present invention as disclosed in the followingdescription. For the purposes of explaining the invention well-knownfeatures of optical technology known to those skilled in the art ofoptical design and visual displays have been omitted or simplified inorder not to obscure the basic principles of the invention. Unlessotherwise stated the term “on-axis” in relation to a ray or a beamdirection refers to propagation parallel to an axis normal to thesurfaces of the optical components described in relation to theinvention. In the following description the terms light, ray, beam anddirection may be used interchangeably and in association with each otherto indicate the direction of propagation of light energy alongrectilinear trajectories. Parts of the following description will bepresented using terminology commonly employed by those skilled in theart of optical design. It should also be noted that in the followingdescription repeated usage of the phrase “in one embodiment” does notnecessarily refer to the same embodiment.

One important feature of the embodiments provided herein is therealization that one way to create a much larger field of view is toparse it into a set of smaller fields of view (each compatible with theoptical limitations of the waveguide) and to (time) sequentially displaythem so fast that the eye perceives them as a unified image.

One way to do this is with holographic elements that can be sequentiallyswitched on and off very rapidly. U.S. Provisional Patent ApplicationNo. 61/687,436, filed 25 Apr. 2012, shows that multiple SBGs can bestacked together in the same waveguide and activated in rapid successionto time-sequentially tile a high-resolution, ultra-wide-field of view.Moreover, each subfield of view has the full digital resolution of theassociated imager, allowing the formation of images that approach oreven exceed the visual acuity limit of the human eye.

While the tiling disclosed in this earlier filing overcomes the twindeficiencies of standard guided-wave architectures (i.e., limited fieldof view and limited pixel resolution), it has limitations when it isnecessary to tile vertically and horizontally over large fields of view.For monochrome displays with modest FOV and expansion in only onedirection, tiling can be accomplished by simply stacking the gratingplanes. However, when the field of view is expanded in both directionsand color is added, the number of layers needed with this approachquickly becomes impractical. For example, consider FIG. 1 which shows isa schematic illustration of a beam defection system for providing adisplay. The display is based on the principle of using a stack 1 ofelectrically switchable gratings SBGs to deflect input light 100 from animage generator 2 into FOV regions or tiles. In one embodiment, each SBGis essentially a planar grating beam deflector that deflects incidentTIR light into output light forming a unique FOV tile. The SBG elements10A-10D provide a first row of four FOV tiles, elements 11A-11D providea second row of four FOV tiles, and elements 12A-12D provide a third rowof four FOV tiles, Advantageously, the image light is collimated and maybe delivered to the SBG stack by, for example, a light guide orSubstrate Guided Optics. The substrates used to containing the SBGs mayprovide the light-guiding substrate. FIG. 2 shows how a horizontal fieldof view can be generated using 4 SBGs 10A-10D configured in fourseparate layers. One input SBG is to provide for directing input imagelight from the image generator into a TIR path. The input imagegenerator may comprise a laser module, microdisplay and optics forcollimation and beam expansion. The output SBGs may be staggeredhorizontally to provide image continuity in FOV space. FIG. 2 shows thelimiting rays in one plane for the SBG group 3 corresponding to one rowof FOV tiles 10A-10D. The limiting rays 101A-101D and the maximumangular extent 01 relative to the normal 102, 103 the display are shown.The rays define the exit pupil 104.

In one embodiment, each subfield of view is limited by the diffractionefficiency and angular bandwidth of the SBG. SBG grating devices mayhave angular bandwidths in air of approximately ±5° (subject to materialproperties, index modulation beam geometry and thickness). In oneembodiment, larger angles can be achieved in practice by using thinnerSBGs. In one embodiment the SBG may have a thickness less than or equalto about 4 μm—e.g., less than or equal to about 3.5 μm, 3 μm, 2.5 μm, 2μm, 1.5 μm, 1 μm, 0.5 μm or smaller. The increased bandwidth resultingfrom thinner SBGs may result in lower peak diffraction efficient. In oneembodiment, it may be desired to increase the refractive indeedmodulation.

In one embodiment, the top SBG 10A provides a field of view of −20° to−10°; the next SBG 10B provides the field of view −10° to 0°; the nextSBG 10C provides the field of view 0° to 10°; the and the lower SBG 10Dprovides the field of view 10° to 20°; one provides the right 20°. Eachoutput put FOV provides a FOV tile of horizontal extent 10 degrees and avertical extent set by the input collimation optics and the waveguidelimitations typically 10 degrees. When the SBG elements are rapidlydisplayed in sequence (SBGs have a switching speed of as little as, forexample, 35 microseconds), the eye integrates the separate opticaloutputs, and a 40° horizontal field of view by 10 degree vertical fieldof view is perceived. Each time a new output SBG is activated the inputimage generator generally indicated by 2 is update with a new digitalimage. In one embodiment, the input image generator provides an image ofapproximately 1000 pixels horizontal by 800 pixels vertical resolution.Hence the complete perceived image has a resolution of 4000×800 pixels.The tiles may abut in FOV space through the exit pupil defined by theoverlapping light rays from the SBG layers. A HMD based on the aboveprinciples is disclosed in a PCT Application No.: PCT/GB2010/000835 withInternational Filing Date: 26 Apr. 2010 by the present inventorsentitled COMPACT HOLOGRAPHIC EDGE ILLUMINATED EYEGLASS DISPLAY (and alsoreferenced by the Applicant's docket number SBG073PCT) which isincorporated by reference herein in its entirety.

The stacking approach shown in FIG. 1 may be suitable for relativelymodest FOV. In one embodiment, horizontal field of view of around 60degrees by 10 degree vertical is feasible. As the field of viewincreases, the number of SBG layers needed becomes impractical: sixlayers is the current practical limit before the performance of thedisplay is compromised by scatter, absorption, and other optical losses.If additional layers for blue and green are added as schematicallyindicated by 13, 14, the number of tiles would be increased by ×3.

One method to avoid using separate RGB SBGs is to use multiplexed SBGs,in which the illumination is provided from opposite ends of thelightguide as R and B/G illumination, compromising the color gamutsomewhat. However, multiplexed gratings raise issues of fabricationcomplexity and cross talk.

One benefit of the embodiments described herein is minimizing the needfor very large numbers of SBG layers. One embodiment providescompressing the stack by interlacing the SBGs, as shown in FIG. 3, asopposed to simply stacking the gratings, as illustrated in FIGS. 1-2.Referring to the simple stacking scheme discussed above (inset), it canbe seen that the optical process which would ordinarily need a stack offour holographic planes to produce one color channel can be accomplishedwith a single layer of interleaved gratings. Note that in FIGS. 1-3, theshading patterns of the holograms is merely for the purposes ofdistinguish the four different types and does not represent the geometryof the gratings.

Turning first to the schematic side elevation view of FIG. 3A, there isprovided an apparatus for displaying an image comprising a multiplicityof groups of selectively switchable beam deflecting elements. In apreferred embodiment, the beam deflectors are SBGs having a firstdiffracting state and a second diffracting state. The first diffractingstate may exhibit high diffraction efficiency and the second diffractionstate may exhibit low diffraction efficiency.

In one embodiment, the SBGs may operate in reverse mode such that theydiffract when a voltage is applied and remain optically passive at allother times. The SBGs may be implemented as continuous SBG laminaseparated by thin (as thin as 100 microns) substrate layers. In oneembodiment, the substrate may comprise plastic. In one embodiment thesubstrate may comprise plastic substrates with transmissive conductivecoatings (instead of ITO).

For simplicity four groups of SBG elements indicated by the numerals15-18 are illustrated, each group comprising four elements labelled bythe characters A-D. The repetition of the pattern of SBG elements isindicated by the dotted line. The number of groups of beam deflectingelements or the number of elements per group is not limited. Theelements are forming in a thin HPDLC grating lamina 15 sandwiched by thetransparent substrates 14A, 14B. Transparent electrodes are applied toopposing faces of the substrates with at least one of the electrodesbeing patterned to overlap the SBG elements.

An input image generator, which will be described in more detail later,provides collimated image light generally indicated by 100. Each groupof beam deflecting elements diffracts image light into a multiplicity ofrays providing a set of FOV tiles. Elements corresponding to a giventile will have a unique grating prescription. The rays may define anexit pupil according to geometrical optical principles. The limitingrays from the group 15 and 18 in the projection of the drawing areindicated by 107, 108. Each element has a diffraction efficiency angularbandwidth ±θ. Comparing FIG. 3 with FIG. 2, it should be apparent thatthe embodiment of FIG. 3 is equivalent to interspersing the SBG layersshown in FIG. 2 within a single SBG lamina. In one embodiment, the firstmultiplicity of beam deflecting elements and the second multiplicity ofbeam deflecting elements are uniformly interspersed a shown in FIG. 3B.In one embodiment, the first multiplicity of beam deflecting elementsand the second of multiplicity beam deflecting elements are randomlyinterspersed as shown in FIG. 3C.

FIG. 3 shows the principles of an HMD. A display based on the aboveprinciples may comprise two sub systems: a color waveguide (which hereinalso refers to a DigiLens) and a device configured to inject an inputimage into the color waveguide (also referred herein to an ImageInjection Node).

The basic principles of the display in one embodiment are illustrated inmore detail using the front elevation views of FIGS. 4-7. In a colordisplay, the DigiLens comprises a stack of three separate RGB waveguideseach providing a red, green or blue color imaging channel. In oneembodiment, each waveguide is further divided into two holographiclayers (to be referred to as a doublet). In one embodiment, thedescription will assume double layers unless stated otherwise. Hence inFIG. 4 the DigiLens 2 comprises the doublet further comprising layers21, 22. The apparatus further comprises the IIN 3, DigiLens driveelectronics 4, and a coupler for admitting light from the IIN into theDigiLens. The IIN and the DigiLens drive electronics are connected bythe communication link 103. Each SBG layer contains arrays of SBGscomprising sets of sub arrays, where the members of any given sub arrayhave one of a predefined set of optical prescriptions, each prescriptioncorresponding to a unique FOV tile. The number of SBG prescriptionsequals the number of FOV tiles. In some embodiments, a prescriptiondefines the Bragg grating geometry needed to deflect incident TIR inputlight from the IIN into output light that defines a FOV tile. Forsimplicity three sub arrays of SBG elements indicated by the numerals200-202 are illustrated. Three elements of each sub array areillustrated labelled by the characters A-C. The drive electronicsprovides voltage outputs 103A-103C. The connections 104A-104C to the SBGelements 300A-300C is shown. The distribution of the array elementsdepends on the FOV tile with, for example, FOV tiles near the centralregion of the FOV needing that the corresponding SBG elements aredistributed near the center of the DigiLens. The spatial configurationof the array elements will be discussed in more detail later. FIG. 5shows input collimated image light 200 from the IIN being coupled intothe DigiLens to provide the collimated image light 201 at the input tothe waveguide 2. Typical collimated output beams from the waveguide forthe SBG sub arrays 200-202 are generally indicated by 202A-202C.

In one embodiment, the SBGs operate in reverse mode such that theydiffract when a voltage is applied and remain optically passive at allother times.

The SBGs may be implemented as continuous SBG lamina separated by thinsubstrate layers (as thin as 100 microns) as shown. This is a planarmonolithic design harnessing the full assets of narrow band laserillumination with monolithic holographic optics. The motivation forconfiguring the SBGs as monochromatic layers is to enable the use ofholographic optics and SBG beam splitter to provide a flat, solid state,precision-aligned display, minimizing the need for bulky refractiveoptics. In one embodiment, the resolution of the display is only limitedby that of the microdisplay. The design is scalable to a larger FOV byinterlacing more tiles in each layer and/or adding new layers. Likewisethe pupil, eye-relief and FOV aspect ratio can be tailored to suit theapplication.

FIG. 6 shows the IIN in more detail in one embodiment. The role of IINis to form a digital image, collimate it, and inject it into theDigiLens. Two separate optical subsystems may be employed: one toilluminate the microdisplay and one to collimate the image. The IIN maycomprise an image processor 3A, input image generator 3B, and a verticalbeam expander (VBE) 3C. The image processor provides image data to theinput image generator via the communication link 150. The imageprocessor also controls the switching of the SBG elements in theDigiLens by means of an electronic link to the DigiLens driveelectronics. The input image generator, which will be discussed in moredetail in the following description, may comprise a laser module andmicrodisplay. Collimated image light 203 from the input generator iscoupled into the beam expander 3C, which is itself optically connectedto the coupler 5. FIG. 7 illustrates the operation of the IIN in furtherdetail concentrating on the input image generator and the VBE andreferring to the XYZ orthogonal coordinate axes provided in thedrawings. The front elevation view corresponds to the YX plane, and theY axes refer to the vertical direction as perceived by the viewer of thedisplay.

The VBE comprises a SBG 60 sandwiched by substrates 61A, 61B. Imagelight from the image generator undergoes TIR, as indicated by 204 withinthe waveguide formed by the substrates. The VBE is designed to be lossy.In other words, the diffraction efficiency of the grating is low at theend nearest the image generator and highest at the furthest extremity.One effect is that it couples light, such as 204A, 204B, out towards thecouple 5 along its entire length providing a vertical beam expansion (inthe Y direction) to match the height of the DigiLens waveguide. Imagelight may be coupled into the VBE by a grating coupler 31A. Referring tothe drawing inset 62, there is further holographic objective 31 and aholographic field lens 32 both optically connected to light guidingdevice 33. Image light from the microdisplay 207 is admitted to thelight bide via the holographic objective and follows the TIR path 208until it is directed out of the light guide into the VBE by theholographic objective 32 as output light 203. In one embodiment, thelight guide 33 includes inclined surfaces at each end. The drawing inset63 shows the configuration of the laser module and microdisplay. Theillumination of the microdisplay 37 may be performed using a diode laser34, a waveguide, and a SBG beam splitter. The SBG beam splitter may beformed as lamina 36 sandwiched between transparent substrates 35A, 35Bforming the waveguide. A slanted SBG grating is recorded in the portionof the lamina 35A overlapping the microdisplay. Collimated P-polarisedlight 210 from the laser module is admitted into the waveguide by acoupler 36. The coupler may be a prism. In some embodiments, the couplermay be a grating device. The coupled light follows the TIR path 211 upthe SBG beam splitter, where according to the properties of SBGs theP-polarised light is diffracted towards the microdisplay. On reflectionthe light becomes S-polarized and passes through the SBG beam splitterwithout substantial loss or deviation to emerge from the waveguide asthe collimated image light 207.

It should be apparent to those skilled in the art of optical design thatmany alternative optical configurations and components may be used toprovide an IIN according to the principles described herein.

For example, the reflective microdisplay could be replaced by atransmissive device. Alternatively, an emissive display may be used. Itshould also be apparent that components such as anamorphic lenses andlight shaping diffusing elements may be used in certain applications tocontrol image aspect ration and illumination uniformity. The apparatusmay further include a despeckler. The IIN may comprise, or be, adiffractive optical device. The processes carried out by the IIN, asemployed in pre-existing techniques, may use several refractive lenses,a polarizing beam splitter cube, and a precision housing for aligningand assembling the various components. Not only are the piece partsexpensive, but the touch labor is excessive. In addition, the wholeassembly is difficult to ruggedize and, in the end, heavy and bulky.Miniaturized components can reduce size and weight, but they alsosharply increase component costs and assembly time.

It should further be apparent that the description of the IIN hasreferred to just one monochromatic microdisplay. In a color display theIIN optical components would need to be replicated for each color. Sincethe optical design uses substrate guided optics and diffractive opticalelements, the combination of the red green and blue channels in oneembodiment can be accomplished within a very compact form factor that isonly limited by the size of the microdisplay and laser module and theoverall system design needs.

The interlacing of the SBG elements in the DigiLens may be carried outin many different ways. For example, the interlaced gratings in theembodiment of FIG. 1 may be configured in the fashion of a Venetianblind (as disclosed in Provisional Patent Application No. 61/627,202 bythe present inventors). However, the MTF associated with such geometryhas notches in it at spatial frequencies traceable to the periodicnature of the interleaving. In one embodiment, introducing a complextessellation of gratings, this deficiency can be rectified.“Tessellation” in at least some embodiments herein is defined as theprocess of creating a two-dimensional surface pattern using therepetition of a geometric shape with no overlaps and no gaps. However,it should be noted that the tessellation pattern is not limited todiamond shaped tessellation patterns of the type illustrated in FIG.4-7. It will be appreciated that patterns based on squares, rectangles,triangles may be used. While a regular patterning is implied in thedrawings, it may be advantageous in certain cases to have a randomlydistributed pattern. In one embodiment, it may also be possible to useelements of different sizes and geometries in a given pattern. Manypossible schemes exist. The elements may have vertically or horizontallybiased aspect ratios. In one embodiment, a broader horizontal aspectratio results in a better horizontal resolution. As will be shown below1.38 mm.×0.8 mm, diamonds give acceptable resolution. Since there is notexpected to be any benefit in having better horizontal resolution thanvertical, it may even be adequate to use 1 mm squares (side on), ratherthan diamonds. For the purposes of mere illustration, the descriptionrefers to tessellated tiling based on diamond shaped or square-shapedelements. In one embodiment of tessellated patterns, there will be asmall gap to allow for electrode addressing circuitry, as will bediscussed later. Examples of SBG element patterning are illustrated inFIGS. 8-10. FIG. 8A shows a tiling pattern 304 comprising rectangularshapes 304A-304F having a multiplicity of vertical and horizontaldimensions. FIG. 8B shows a tiling pattern 305 known as Penrose tilingcomprising elements 305A-305J. FIG. 8C shows a tiling pattern 306 basedon regular hexagons comprising elements 306A-306C. FIG. 8D shows atiling pattern 306 based on squares comprising elements 307A-306D. FIG.9A shows a tiling pattern 308 based on diamond shapes comprisingelements 308A-308D. FIG. 9B shows a tiling pattern 309 based onisosceles triangle shapes comprising elements 309A-309D. FIG. 10A showsa tiling pattern 310 based on horizontally elongated hexagons comprisingelements 310A-310C. FIG. 10B shows a tiling pattern 311 based onrectangles with horizontally biased aspect ratios comprising elements311A-311D. FIG. 10C shows a tiling pattern 312 based on rectangleshorizontally elongated diamond elements 312A-312D.

In one embodiment, the technology used for fabricating SBG arraysregularly produces features as small as 50 microns (500 dpi), so thatinterlacing features in the manner described above is not an issue. Oneimportant condition is that the distance between gratings of likeprescription should be small compared to the size of the eye pupil underbright conditions (assumed to be 3 mm in bright sunlight). In oneembodiment, when this condition is met, banding is not observable.Importantly, in one embodiment as the eye moves around in the eye box,light lost from a band moving beyond the pupil of the eye is offset bylight gained from another band moving into the pupil. The luminosityvariation anticipated from this effect, assuming uniform illuminationacross the waveguide, is approximately ±1% of the average brightnesslevel. The concept of banding may be most readily understood inembodiments where the SBG elements comprise columns. However, the basicprinciple may apply to any type of patterning that may be used with anyembodiments described herein.

In some embodiments, image light is admitted into one end of theDigiLens only. Each waveguide in the DigiLens may generally comprise twoSBG layers. It should be apparent from consideration of the drawings anddescription that in such embodiments the layers may comprise SBG arraysof identical prescription with one reversed and the image injection nodebeing configured in two symmetrical portions to provide separate imagelight in opposing paths to the two holographic layers. Such embodimentsmay need duplication of components and are therefore likely moreexpensive to implement.

In some embodiments, each DigiLens doublet waveguide is 2.8 mm thick.The SBG layers may in theory be separated by low index substrates or airgaps. In one embodiment, in many practical applications that need TIRbeam geometry cannot be supported without an air interface. Note alsothe thickness of the holograms has been exaggerated. In one embodiment,the gratings may be 3 microns in thickness sandwiched by substrates ofthickness 100-200 microns. The thicknesses of the transparent electrodesapplied to opposing faces of the substrates are measured in nanometers.

FIG. 11 is a schematic cross-sectional view of a DigiLens waveguidecomprising two layers 20, 21 in one embodiment. Layer 20 comprisestransparent substrate 20A, transparent patterned electrode layer 20B,SBG array 20C containing elements such as 20F, a transparent electrodelayer 20D, and a second substrate 20E. Layer 21 comprises transparentsubstrate 21A, transparent patterned electrode layer 21B, SBG array 21Ccontaining elements such as 21F, a transparent electrode layer 21D, anda second substrate 21E. In one embodiment, the substrates 20E and 21Amay be combined into a single layer.

FIGS. 12A-12D shows examples of tessellation patterns in the regionscontaining SBG elements of types labelled 1-4. The eye pupil 311 isoverlaid. FIGS. 13-14 shows MTF data for one particular SBG element typeconfigured as shown in FIG. 13 at one eye pupil location in the displayexit pupil. The SBG elements are labelled by 313A-3131. FIG. 14 showsthe MTF curves. In this embodiment, the upper curve 314A is thediffraction limited MTF, and the lower curve is the estimated SBG arrayMTF allowing for aberrations. The diamond shapes are based on trianglesof triangles of side=0.8 mm, and therefore, length=1.38 mm. Thisarchitecture is applicable to a 2 layer (1 doublet) monochrome design,or a single color layer in the R, G, B color design. Three stackeddoublet layers give the composite performance. The exit pupil 311 is 3mm in diameter in this embodiment.

The DigiLens architecture corresponding to FIGS. 13-14 tiles 12 SGBelements on 2 monochromatic SBG layers. Referring to FIG. 18, the firstlayer, which is illustrated in FIG. 13, tiles all of the horizontal(lower) tiles: L1-4 and the horizontal (middle) tiles (MID,1), (MID,2).The second layer tiles the horizontal (middle) tiles: (MID,3), (MID,4),and all of the horizontal (upper) tiles: U1-4.

FIG. 15 shows an example of tiling using rectangular SBGs withhorizontally biased aspect ratios. The tiling pattern 315 compriseselement types 1-5 also labelled by the numerals 315A-315E.

FIG. 16 illustrates in one embodiment how the DigiLens tiles the FOV inthe exit pupil in three consecutive stages of the formation of amonochromatic image. The writing of images of each primary color willfollow a similar process. FIGS. 16A-16C show three types of SBG 1-3 alsoindicated by the labels 315A-315C being activated. The eye pupil 311 andthe exit pupil 316 are overlaid in each case. The corresponding FOVtiles 319A-319C in FOV space indicated by the rectangle 319 are shown inFIGS. 16D-16F. Only a small number of SBG elements are illustrated tosimplify the understanding of the switching process. Note that all SBGelements of a given type can all couple light out simultaneously owingto the “lossy” coupling between the beam and grating. In other words,the diffraction efficiency of individual elements is modulated toextract a fraction of light the light available from the guided beam. Inone embodiment, the first elements the guide beam interacts with havethe weakest coupling efficiency, while the elements at the otherextremity of the beam path have the strongest.

The area of the pupil filled by light from SBGs of a given type isroughly fixed. As the eye moves from left to right, light is lost fromthe leftmost SBG elements, but is gained on the right hand edge. Theluminosity variation arising from this effect, assuming uniformillumination across all elements, is approximately 2% (+/−1% of theaverage brightness level).

In some embodiments, the periodicity of the SBG elements could yieldunwanted artifacts resulting from diffraction by the element aperturesor even interference effects. The latter is believed to be unlikelybecause light propagating in the planar waveguide structure will notnecessarily be in phase with light from the next aperture because of theunequal optical path lengths inherent in planar waveguide structures.Light exiting each periodic aperture is therefore expected to combineincoherently (even if the coherence length of the laser is reasonablylong with respect to the planar waveguide structure) when consideredacross all SBG elements. In the event that an unwanted artifact doesarise from the SBG element, periodicity on the proposed strategy wouldinvolve randomizing the elements.

Points across the DigiLens aperture contribute angular information tothe 10 mm eye box progressively differently because of the 25 mm eyerelief. Points towards the left of the display do not contribute angularcontent from the right of the FOV, and vice versa. To maximize opticalefficiency, the DigiLens in one embodiment may be optimized to fill thedesired eyebox at the prescribed eye relief. FIGS. 10A-10D indicate theportions of the SBG aperture that contribute to the eyebox in oneembodiment.

Not all positions across the surface of the DigiLens contribute pupilfilling content at the eyebox. To fill the 10 mm pupil at 25 mm (eyerelief), the minimum size of the outcoupling SBG is just less than 30 mmwide. However, only a very small region in the center of the DigiLensprovides content at all field angles, e.g.: −15°±5°, −5°±5°, +5°±5° and+15°±5°. These angular bands correspond to outcoupling SBG columns 1, 2,3, and 4 (found for each of Upper)(+10°, Mid) (+0° and Down)(−10°fields).

FIG. 17 shows the distribution of SBG tile types for the 3 vertical×4horizontal FOV tiling pattern of FIG. 18. As shown in the drawing inthis case all 12 SBG prescriptions are needed in the centre of the FOV,while the number needed falls to just one at the horizontal limits ofthe FOV

FIG. 18 shows an exemplary FOV tiling pattern that may be used to tile a52°×30° FOV (assuming each SBG prescription provides 13°×10°). A totalof 12 different types of SBG prescriptions need to be providedcomprising “UP”, “MIDDLE” and “DOWN” elements for vertical tiling andfour horizontal tiling prescriptions for each of the vertical tilingSBGs tiles (labeled 1-4). Each type of SBG will be represented by morethan one SBG element. Hence to view the FOV tile at [UP,1], it is neededto sequentially activate each element “1” in each column group “UP” inthis embodiment.

FIGS. 19-23 illustrate SBG patterns, which correspond to each of thetiling regions defined in FIGS. 17-18. In each case, the single layerpattern and two overlaid patterns for on SBG type are illustrated.Square elements have been assumed in this embodiment. FIG. 19 showspatterns corresponding to regions 1 and 7 (3 tile types). The two layersare indicated by 326, 327, each layer comprising type 1 elements 326A,327A and spaces 326B, 327B (to be occupied by elements of other types).In this case, one layer achieves 33% aperture fill and one doubletachieves 66% aperture fill. FIG. 20 shows patterns corresponding toregions 2 and 6 (6 tile types). The two layers are indicated by 328,329, each layer comprising type 1 elements 328A, 329A and spaces 328B,329B. In this case, one layer achieves 16.7% aperture fill and onedoublet achieves 33% aperture fill. FIG. 21 shows patterns correspondingto regions 3 and 5 (9 tile types). The two layers are indicated by 330,331, each layer comprising type 1 elements 330A, 331A and spaces 330B,331B. In this case, one layer achieves 11.1% aperture fill and onedoublet achieves 22.2% aperture fill. Finally, FIG. 22 shows patternscorresponding to region 4 (12 tile types). The two layers are indicatedby 332, 333, each layer comprising type 1 elements 332A, 333A and spaces332B, 333B. In this case, one layer achieves 8.33% aperture fill and onedoublet achieves 16.7% aperture fill.

The resulting composite pattern 340 is shown FIG. 23. An example of thecoverage of a single SBG type in a three layer waveguide 341 is shown inFIG. 24.

FIGS. 25-26 show SBG patterns for each layer of a two layer waveguide inone embodiment.

A typical estimate of the human visual acuity limit is about 1 arcminutes/line pair=60 cyc/deg; this is a generally accepted performancelimit and equates to 3.4 cyc/mr. This can be achieved with 20/20 visionunder bright conditions where the eye pupil is constricted to 3 mmdiameter. The eye is photoreceptor limited. Cone spacing at the foveacan be as small as 2.5 equivalent to 60 cyc/deg. At larger pupilapertures, the eye's performance degrades significantly due toaberration in the eye. At about 3 mm, the eye's performance is close todiffraction limited. It is noted that diffraction limit cut off at 532nm for an f/5.6 eye (3 mm pupil with f=17 mm) is about 320 lp/m, whichis significantly higher than the retina limit. The eye is thereforephotoreceptor density limited in this embodiment. In considering this,it is realized that if the eye's pupil, or the display limiting theeye's pupil, is greater than 0.75 mm (equates to 1.4 cyc/mr cut off),then the blur spot size at the retina will not be affected. Thisestablishes a minimum aperture requirement for the display. A 12 μmpitch LCoS microdisplay with 4H×3V tiles, where each tile has 640H×480Vpixels may yield 2560H×1440V pixels over 52 degH×30 degV. The displayprojection magnification from the microdisplay to the retina isapproximately 2. Hence the angular size of the microdisplay pixels atthe eye is 6.0 μm giving a display 83 cyc/mm Nyquist frequency at theretina (1.4 cyc/mr). Image sharpness may be assessed to be sharp whencontrast is maximized (and is high) at the half Nyquist limit (i.e.,about 40 cyc/mm in the following plots showing image quality at theretina).

The concern that the periodic structure of the Color Waveguide SBGLayers will act as a diffraction grating has been addressed. Many of thepotential sources diffractive artifacts in the Color Waveguide, such ashigher order diffraction, zero orders beams in the waveguide, and theapertures of the SBG elements, may be minimized (or even eliminated) oncloser inspection SBGs are Volume Bragg gratings, and in one embodimentmay not support higher orders as would be found with blazed or thingrating. The absence of higher orders may minimize (or even eliminate)ghost images. In one embodiment, within the waveguide light whichcontinues to be wave guided (in the lossy waveguide) will not ‘see’ theoutput apertures of the tiles. Build-up of diffraction orders within thewaveguiding beam will therefore not occur. Light output from differentSBG element apertures will not be in phase (apart from perhaps in aunique case). The optical path will change as a function of field angle.It is therefore reasonable to expect the outputs from the apertures tobe out of phase, and therefore to combine incoherently. Diffractiveartifacts are therefore not anticipated.

Earlier concerns about the periodic structure were based on 50 um columnwidths. The new SBG feature sizes are now in the range 800 um to 1380um. Diffraction angles predicted by the grating equation aresignificantly smaller. For example, for 50 um features with a 52° inputangle, the diffraction angle would be 1 degree (equivalent to 74pixels). For 1000 um features at 52° input angle, the diffraction anglereduces to 0.05° (3.7 pixels). In the very worst case, in thisembodiment, if a diffractive ghost appears under conditions of say, avery bright object against a dark background, it will appear like nearobject lens flare, and not as a double image well separated from theoriginal.

Although a despeckler may be incorporated into the IIN to overcome laserspeckle, there is a reasonably high expectation that the design isinherently despeckled. Phase diversity should exist across the outputSBG apertures. Polarization diversity will further assist with thedespeckling, and hence minimize the effects of any diffractive artifactsfrom the structure. As a further safeguard, noting that it is notessential to have straight edges on the SBG apertures, the edges will bepatterned to randomize any artifacts.

Several factors may influence design layout. It may be needed to takeinto account tessellation limitations to maximize pupil fill.Importantly, it may be needed to have 3, 6, 9, and 12 tile each patternon 2 layers of a single doublet, and create a maximized pupil fillcondition for any position in the display exit pupil for a 3 mm diameterprojected eye pupil. The offsets between the SBG patterns in the twolayers need not have a non-integer offset to tessellation pattern designin x or y. In one embodiment, an x offset will in effect cause a halfpixel on one side or another of a region, and would then need ITOaddressing for half of a pixel in that area alone. In one embodiment, itis better to avoid this to retain a uniform addressing pitch. In oneembodiment, an offset in y of the pattern would similarly need halfpixel vertical addressing. Similarly, it would be desirable to avoidthis. It is acceptable to have a half pixel offset in y to maximizecoverage, but then all patterns need to have half pixel offset in samedirection. In one embodiment, all 12 tile types are employed on eachdoublet. However, the maximum tile type fill is obtained for 9 tilestypes on two layers. We also have cases where 6 tile types and 3 tiletypes need to be configured, for example, on two layers. Consider, forexample, a region where three horizontal tile types to fill eye pupilfor a single vertical tile band in one embodiment. Note that otherlayers of doublets address the other two vertical tile bands. Layers 1and 2 both contain the same tiles, but in an offset arrangement toachieve the desired pupil filling. A single tile has dimensions:(H,V)=(0.8*sqrt(3), 0.8)=(1.386, 0.8). The offset on a single layer of 1tile type is given by: (dx,dy)=(0,3V). The offset of layer 1 withrespect to layer 2 is given by: (dx,dy)=(0.5H, 1.5V)=(0.693, 0.4). Inthe analysis that follows, 1 mm×1 mm squares have been used to simplifythe optical modeling; however, the principles are identical no matterthe shape. However, it should be noted that certain shapes will packpreferentially.

FIGS. 27-29 illustrate some embodiments of the IIN comprising a inputimage generator comprising the diode laser module 34, coupling prism34A, SBG beam splitter layer 35 sandwiched between substrates 35A, 35B,microdisplay module 38, light guide 41 contain include surfaces 42A,42B, input coupling, holographic objective, spacer half wave plate,holographic field lens.

Advantageously, in one embodiment the IIN provides a telecentric(slightly projected) pupil to allow better coma control and betterpackaging with the pupil vertical beam expander.

FIG. 28A is a cross sectional view illustrating the coupling from theInput Image Node to the DigiLens via the VBE in one embodiment. FIG. 28Bshows a detailed ray trace of the embodiment of FIG. 28A. The VBE maycomprise, or is, a lossy grating extracting light from the beam over adistance corresponding to the height of the DigiLens. At the objectiveinput, the light is well ordered in that light across the pupil isarranged in tight field bundles. At the far end of the VBE, thedifferent numbers of bundles of light with different field angles maycause the bundles to be more distributed. At the objective end, the pinkray with the highest waveguide angle may be furthest from the rest ofthe VBE waveguide. The steepest ray in waveguide starts furthest to theleft. This may help keep the passive input coupler (and VBE thickness)down. At the far end (fully to the left) coupling out of the VBE intothe waveguide is hampered by the loss of order, as found at the input.To prevent a doubling in the thickness of the waveguide, a 50/50 activecoupler is used in one embodiment at the VBE to DigiLens coupling stage.

FIG. 29 is a plan view of the DigiLens and the VBE showing how thelatter is split into two switchable elements. This reduces the waveguidethickness. Each DigiLens doublet waveguide is 2.8 mm thick. Without theswitch, the thickness doubles such that the total waveguide thicknessincreases from around 10 mm, to about 18 mm. FIG. 10 shows rays tracedfrom the VBE to the DigiLens.

Several embodiments provided herein may have to be well suited forsubstrate guided optics. First, component costs may be reduced. Theoptical complexity is contained in the various holographic opticalelements. Once the non-recurring engineering (NRE) associated withcreating a set of masters is complete, the replication costs arerelatively insignificant, as compared to the recurring material costsassociated with discrete refractive components. Second, assembly timemay be reduced. Not only is part count reduced, but the assembly processis also much faster. The planar structures can be cost-effectivelylaminated together with very high optical precision using alignmentfiducials. The touch labor is greatly reduced, as compared to that ofbuilding a piece-part assembly to exacting standards. Third, the opticalprecision is greater. One of the biggest challenges in designing a newoptical design is controlling the roll-up of tolerances on the pieceparts, the mechanical housings, and the assembly procedure. Withholographic optical elements (HOEs), “gold standards” can be assembledby senior engineers and this level of quality captured in the HOEmasters during the NRE phase. Beside the fact that optical alignment ofthe HOEs can be accomplished with great precision, the individual HOEsare more tolerant of variations in alignment. Thus, the overall yield ofhigh quality devices is much higher. Lastly, size and weight are greatlyreduced by this monolithic design, as is the ruggedness of the entiresubsystem.

One important performance parameter is the see-through transmission ofthe display. The variables that have an impact on transmission are theITO coating (0.995), the AR coatings (0.99), and the absorption of thesubstrates and holographic layers. There will also be Fresnel losses atthe interfaces between the waveguides and the low-index bonding layers.In one embodiment, the desired transmission for the color displayis >70%, with an objective of >90%. Assuming three waveguides perdisplay and two substrates per waveguide, the calculated transmission is93%, meeting the stipulated objective. In one embodiment, the designdescribed herein may use 100-micron glass substrates. With threewaveguides and three substrates per waveguide (note: two holographiclayers may need three substrates), the total thickness of the display ofthe color display may be still less than 1 mm. The thicknesses of theholographic layers (including the coatings) are negligible; eachcontributes only 4-5 microns to the overall thickness. Since weight isalways an issue, this may be an important feature of the embodimentsdescribed herein. In one embodiment where the substrate comprisesplastic, the weight may be further reduced.

In one embodiment, the SBGs operate in reverse mode such that theydiffract when a voltage is applied and remain optically passive at allother times. The SBGs may be implemented as continuous SBG laminaseparated by thin (as thin as 100 micron) substrate layers as shown.Ultimately the design goal is to use plastic substrates withtransmissive conductive coatings (to replace ITO). Plastic SBGtechnology suitable for the present application is being developed in aparallel SBIR project. In this embodiment, this is a planar monolithicdesign harnessing the full assets of narrow band laser illumination withmonolithic holographic optics

Configuring the SBGs as monochromatic layers may enable the use ofholographic optics and SBG beam splitter technology to provide a flatsolid state precision aligned display totally eliminating the need forbulky refractive optics. The resolution of the display is only limitedby that of the LCoS panels.

The design is scalable to a larger FOV by interlacing more tiles in eachlayer and/or adding new layers. Similarly, the pupil, eye-relief, andFOV aspect ratio can be tailored to suit the application. The design canbe scaled down to a smaller FOV.

FIGS. 30A-30B illustrate a scheme for polarization recycling for usewith at least some embodiments described herein. This may be relevant inthe event that polarization is not maintained with an SBG outcouplingwaveguide, either by virtue of the properties of the SBG material(current or one developed in future), or where a polarization rotationcomponent is deliberately introduced in the waveguide. Specifically, athinner DigiLens waveguide can be used if linearly polarized light isinput into the DigiLens waveguide (i.e., light coupled from VBE into thewaveguide), and light is converted to a mixture of S and P polarizedlight. This may allow up to a factor of two times reduction thinness ofthe waveguide. FIG. 30A shows a waveguide 252 with input rays 354A, 354Bdirected into the TIR paths labelled by 355A, 355B by a coupling grating353. The light may be of any polarization. However, for a SBG inputgrating P-polarzation may be desirable in one embodiment. The couplinggrating aperture is A. For only explanation purpose, the TIR angle hasbeen chosen to be 45° so that the thickness of the waveguide requiredfor the limiting input ray to just skirt the edge of the couplinggrating after the first TIR bounce is A/2.

Referring to FIG. 30B, the waveguide 356 has input coupling opticscomprising the first and second gratings 357A, 357B disposed adjacenteach other, the half wave film 357C sandwiched by the waveguide and thefirst grating; and a polarizing beam splitter (PBS) film 357D sandwichedby the waveguide and the second. The PBS is design to transmitP-polarized light and reflect S-polarized light. Again the TIR angle ischosen to be 45° only for illustration purpose. Input P-polarizedcollimated light 358A, 358B is coupled in to the waveguide via the firstgrating and half wave film (HWF) to provide S-polarized light 359A, andvia the second grating and PBS to provide P-polarized light 359C, 359D.Comparing the embodiments of FIG. 30A and FIG. 30B, it should beapparent that in the second the input coupling aperture can be the equalto the length of two TIR bounces owing to the polarization recovery bythe HWF and PBS. In the embodiment of FIG. 30A. the input couplet cannotbe longer than one TIR bounce because grating reciprocity would resultin the light being diffracted downwards out of the waveguide. Onebenefit of the embodiment of FIG. 30B is that the waveguide thicknesscan be reduced by 50%; that is, for a coupler length equal to A thewaveguide thickness (for 45° TIR) is A/4. At this in some embodiments, Sand P lights in the waveguide are not separated. Typically, the inputlight will be divergent resulting in the S and P light quickly becomingspatially mixed. However, if the waveguide rotates the polarization,because more P is out coupled, there will be more conversion of S to Pthan P to S, thus yielding a net gain. The polarization rotation mayarise from the reflective characteristics of the waveguide walls andfrom the birefringence of the holographic material where SBGs are used.In one embodiment, polarization rotation is provided by applying aquarter wave film (QWF) to the lower face of the waveguide. HWFs andQWFs may be about 0.125 mm thick. A typical adhesive layer may be about75 microns. Hence in some embodiments, the polarization control films donot contribute significantly to the overall waveguide thickness. Incertain cases the films can be can be immersed in an adhesive layer usedfor lamination.

FIG. 31 illustrates a counter-propagation waveguide for use in someembodiments. The waveguide comprises adjacent grating laminas 51A, 51Bof identical but opposing prescriptions sandwiched by substrates 52A,52B. Wave guided light 362 propagating from left to right interacts withthe grating 51A to provide continuously extracted light 360A-360C toprovide the expanded output beam 360. Wave guided light 368 propagatingfrom right to left interacts with the grating 51B to providecontinuously extracted light 361A-361C to provide the expanded outputbeam 361. Note that a small amount of light that is not extracted fromeach of the left/right propagation directions will interact with anopposing grating and get diffracted out of the grating in the oppositedirection to that of the expanded beams 360, 361, as indicated by therays 363-366.

FIG. 32 illustrates the use of a beam splitter in a waveguide in oneembodiment to achieve uniformity. This principle may be applied bothexpansion axes. As a further refinement, a beam splitter offset may beemployed in waveguide (i.e., not in middle of waveguiding surfaces, butoffset from waveguide midpoint to maximize uniformity following multiplebounce interactions). A yet further refinement is to use differentreflectivities in beam splitter to optimize and tailor beam mixing. Notto be bound by any particular theory, but by varying the reflectivity %of the beam splitter to something other than 50/50, or by varying thetransmission/reflection split along a B/S length, the pupil fill can behomogenized and optimized. For example, in FIG. 32 the waveguide 353contains a beam splitter layer 352. In some embodiments, the beamsplitter may be provided using a thin film coating. A TIR ray such as370 may then undergo beam splitting, which results in waveguidingoccurring between the upper and lower walls of the waveguide; betweenthe upper wall of the waveguide and the beam splitter, and between thebeam splitter and the lower wall of the waveguide as indicated by rays371-373.

The IIN stop is formed by controlling the profile of the inputillumination. In at least some embodiments there is no hard physicalstop in the projection optics. The benefits of projected stop includedecreased waveguide thickness. The stop is projected midway up the VBEto minimize aperture diameter within the VBE, and hence minimizing theaperture width of the VBE to DigiLens waveguide coupler (e.g., reducingthe width of the 1^(st) axis expander) limits the thickness of the2^(nd) axis expansion optic.

FIGS. 33-36 show details of an ITO in some embodiments addressingarchitecture for use in a DigiLens.

FIG. 33 shows a method of reducing the number of tracks in a given ITOlayer, which method uses dual sided addressing of ITO, and super pixeladdressing to reduce the number of tracks by approximately one third.The pixels are provide in a first group 35, 0 comprising: elements ofdimension 3 units×1 unit such as the ones labelled by 350A, 350B; andelements of dimension 1 unit×1 unit, such as the ones labelled350C-350H, and a second overlapping inverted group 351 of identicalpixel geometry as indicated by 351A-351G.

FIGS. 34-36 show how interleaving of electrode wiring tracks may be usedto permit a 2D electrode structure to address (switch) multipledifferent tessellation types. FIG. 34 shows a wiring scheme used inembodiment, in which electrode elements such as 401 are connected bytracks 402-404. FIG. 35 shows a wiring scheme in another embodiment withelectrodes 407-409 and track portions 410, 411 indicated. FIG. 36 showsthe electrodes and tracks of the embodiment of FIG. 33 in more detailswith the elements and tracks indicated by the numerals 421-434.

The electrode architecture may benefit in terms of reduction of partcomplexity from using identical pattern technique, and flip symmetry tocreate full addressing network. This is not needed to make design work,but may limit number of parts that need to be designed and handled.

In one embodiment, a graduated reflection profile underneath SBG layeris used to control (or assist) with grating DE variation along length(normally achieved in SBG grating using index modulation). This may beuseful in cases such as the VBE where low percentage of light is outcoupled in the first bounce, but high percentage is coupled out at theother end of the expander.

In one embodiment, 1D expansion engines are used to double input powerand/or minimize 1D aperture width.

In one embodiment, the display is configured as a “visor”. The colorwaveguide is curved in at least one plane. In general, such anembodiment may have a large (30 mm) eye relief and a large exit pupil.The large exit pupil may reduce (or even eliminate) the need for IPDadjustment. FIG. 37A-37B are schematic plan and side elevation views ofa curved visor comprising a DigiLens 71 and optical-electronic modules70A, 70B to either sides. One module will comprise the IIN. The secondmodule may contain auxiliary optics and electronics.

FIG. 38 shows the DigiLens of a curved visor in one embodiment in moredetail. The DigiLens may comprise laminated waveguides, each containingSBG arrays 73A-73C. In this case the three SBG layers are isolated fromeach other by the cladding layers 72A-72D. The ray paths are indicatedby 381A-381C. In the embodiment of FIG. 39, the SBG layers are stackedwithout cladding layers to form a single waveguiding structure. The raypaths are indicated by 382A-382C.

In one embodiment as shown in FIG. 40, a visor DigiLens is shapedfacetted planar elements 76A, 76B allowing the waveguides to be planar.As shown in the insets B and C, gratings 77A, 77B are provided at theoptical interfaces 77 between the facets to control the beam angles toensure efficient coupling of guided image light to the SBG arrayelements. The gratings 77A, 77B may be Bragg gratings. In one embodimentas shown in FIG. 41, a facetted DigiLens comprising planar facets, suchas 76A, 76B, is embedded with a curved lightguide 79.

The embodiments may rely on monochromatic waveguides. However it shouldbe apparent from consideration of the description that in alternativeembodiments the waveguides could operate on more than color. Suchembodiments may involve a more complicated IIN design.

In at least some embodiments the multilayer architectures describedherein may not be used with conventional holograms, because they wouldinterfere with each other. Thus, SBG, which can be switched clear toallow time-domain integration of the field of view, may be employed toovercome this challenge.

One embodiment described herein is related to a HMD, such as one withthe following specification:

-   -   a) 180° see-through visibility;    -   b) full color;    -   c) 52°×30° FOV;    -   d) 30 mm×30 mm eye box;    -   e) 2560×1440 resolution;    -   f) Snellen 20/20 acuity;    -   g) 30 mm eye relief;    -   h) universal IPD;    -   i) binocular; and    -   j) polycarbonate optics.

One important feature of at least some of the embodiments describedherein is that they provide the benefit of see-through. The latter is ofgreat importance in Head Up Displays for automobile, aviation and othertransport applications; private see-through displays such for securitysensitive applications; architectural interior signage and many otherapplications. With the addition of a holographic brightness enhancingfilm, or other narrow band reflector affixed to one side of the display,the purpose of which is to reflect the display illumination wavelengthlight only, the see-through display can be made invisible (and hencesecure) in the opposite direction of view. The reflected displayillumination may be effectively mirrored and therefore blocked in onedirection, making it desirable for transparent desktop displayapplications in customer or personal interview settings common in bankor financial services settings.

Although some of the embodiments above describe wearable displays, itwill be clear that in any of the above embodiments the eye lens andretina may be replaced by any type of imaging lens and a screen. Any ofthe above described embodiments may be used in either directly viewed orvirtual image displays. Possible applications range from miniaturedisplays, such as those used in viewfinders, to large area publicinformation displays. The above described embodiments may be used inapplications where a transparent display is desired. For example, someembodiments may be employed in applications where the displayed imageryis superimposed on a background scene such as heads up displays andteleprompters. Some embodiments may be used to provide a display devicethat is located at or near to an internal image plane of an opticalsystem. For example, any of the above described embodiments may be usedto provide a symbolic data display for a camera viewfinder in whichsymbol data is projected at an intermediate image plane and thenmagnified by a viewfinder eyepiece. One embodiment may be applied inbiocular or monocular displays. Another embodiment may also be used in astereoscopic wearable display. Some embodiments may be used in a rearprojection television. One embodiment may be applied in avionic,industrial and medical displays. There are applications inentertainment, simulation, virtual reality, training systems and sport.

Any of the above-described embodiments using laser illumination mayincorporate a despeckler device for eliminating laser speckle disposedat any point in the illumination path from the laser path to theeyeglass. Advantageously, the despeckler is an electro-optic device.Desirable the despeckler is based on a HPDLC device.

REFERENCES

The following patent applications are incorporated by reference hereinin their entireties:

U.S. Provisional Patent Application No. 61/627,202 with filing date 7Oct. 2011 by the present inventors entitled WIDE ANGLE COLOR HEADMOUNTED DISPLAY which is also referenced by the Applicant's docketnumber SBG106;

PCT Application No. US2008/001909, with International Filing Date: 22Jul. 2008, entitled LASER ILLUMINATION DEVICE; PCT Application No.US2006/043938, entitled METHOD AND APPARATUS FOR PROVIDING A TRANSPARENTDISPLAY;

PCT Application No. PCT/GB2010/001982 entitled COMPACT EDGE ILLUMINATEDEYEGLASS DISPLAY; PCT Application No. PCT/GB2010/000835 withInternational Filing Date: 26 Apr. 2010 entitled Compact holographicedge illuminated eyeglass display;

PCT Application No. PCT/GB2010/002023 filed on 2 Nov. 2010 entitledAPPARATUS FOR REDUCING LASER SPECKLE; U.S. Patent Application: Ser. No.10/555,661 filed 4 Nov. 2005 entitled SWITCHABLE VIEWFINDER DISPLAY;

U.S. Provisional Patent Application No. 61/344,748 with filing date 28Sep. 2010 entitled Eye Tracked Holographic Edge Illuminated EyeglassDisplay;

U.S. Provisional Patent Application 61/573,066 with filing date 24 Aug.2011 by the present inventors entitled HOLOGRAPHIC POLYMER DISPERSEDLIQUID CRYSTAL MATERIALS AND DEVICES;

U.S. Provisional Patent Applications No. 61/457,835 with filing date 16Jun. 2011 entitled HOLOGRAPHIC BEAM STEERING DEVICE FOR AUTOSTEREOSCOPICDISPLAYS; PCT Application No. US2008/001909, with International FilingDate: 22 Jul. 2008, entitled LASER ILLUMINATION DEVICE;

PCT Application No. PCT/GB2010/002023 filed on 2 Nov. 2010 by thepresent inventors entitled APPARATUS FOR REDUCING LASER SPECKLE;

U.S. Provisional Patent Application No. 61/573,121 with filing date 7Sep. 2011 by the present inventors entitled METHOD AND APPARATUS FORSWITCHING HPDLC ARRAY DEVICES which is also referenced by theApplicant's docket number SBG105B;

PCT Application No. PCT/GB2010/000835 with International Filing Date: 26Apr. 2010 entitled COMPACT HOLOGRAPHIC EDGE ILLUMINATED EYEGLASS DISPLAY(and also referenced by the Applicant's docket number SBG073PCT); and

U.S. Provisional Patent Application 61/573,082 with filing date 29 Aug.2011 by the present inventors entitled CONTACT IMAGE SENSORS.

Micro-Tessellations

One set of embodiments uses Micro Tessellations. The performance ofmicrotessellations gratings in the context of a Switchable Bragg GratingDigiLens™ waveguide device will now be explored. Tessellation is apattern of repeating shapes that fit together without gaps. Use of theterm ‘tessellation’ may refer to a single element of a tessellationpattern. In the practical application of tessellations pertaining toDigiLens™ devices tessellation also means the creation of patternswithout substantial gaps between tessellation elements—i.e., where thereis high overall aperture fill factor.

A tessellation element is a region (aperture) of diffraction grating ordiffraction gratings, which may be a switchable diffraction grating(SBG). The tessellation will diffract light over all regions of thetessellation at the same time. The diffraction grating may be switchableor non-switchable.

Micro-Tessellation: this is a small tessellation that exists within alarger primary tessellation element. The microtessellations within aprimary tessellation may have different grating prescriptions.Micro-tessellation elements that exist within a primary tessellationelement all diffract at the same time. The performance of tessellationsand their impact on MTF has been described in earlier documents, whereina single grating was written into the tessellation.

Microtessellations within a Primary Tessellation Structure

Performance considerations of interest are: MTF (resolution) anduniformity of field angles.

In a tiled substrate guided (SGO), a single field of view will exist inthe waveguide. At any given moment in time, this will carry field ofview information for a portion of the overall field of view. In the caseof an eye display, this is a portion of the projected field that is outcoupled from the SGO. The out-coupling gratings need to out-couple thisfield of view content such that the eye can see this field of viewinformation across the eye box, desirably with the same flux enteringthe eye for each field angle and for all field angles at any position ofthe eye pupil within the eyebox. From earlier work it is recognized thatlarger tessellations yield superior MTF (resolution) performance, andfield of view irradiance on the eye's pupil is more uniform with smallertessellations. Outcoupling gratings angular bandwidth leads to a falloff in the output light with field angle. A minimum tessellation size toyield sufficient resolution is dependent on the system resolutionsought. However, a minimum tessellation aperture size of 0.5 mm to 1 mmwidth (or diameter) will approximately be needed to support 0.7 to 1.4lp/mr resolutions, with larger apertures being preferred in oneembodiment. This particularly affects high spatial frequencyperformance.

A tessellation is a region of the out-coupling grating that, when in adiffracting state, will diffractively out-couple the light at all pointsin that tessellation aperture region at the same time. The regionswithin a tessellation may contain with one grating prescription or aplurality of grating prescriptions. This plurality of gratingprescriptions may be achieved either by multiplexing the gratings(grating prescriptions share the same area of the tessellation), or byhaving spatially discrete regions of the tessellation into which iswritten a single grating only. A microtessellation is small tessellationthat is switched at the same time as other small tessellation areas. Thecase of spatially discrete micro-tessellations (J) is examinedfollowing.

μT gratings may be designed to have angular bandwidth overlap with theneighboring μTs (in angular field). Modeling micro-tessellations for agiven field angle in one embodiment is described below. One case toconsider is FoV overlap of micro-tessellations causing different fieldangles to be output at different points. Another case to consider isequal irradiance of eye pupil from multiple micro-tessellations for agiven field angle. Some field angles would output light equally frommultiple micro-tessellations, thereby providing the same irradiance ofthe eye pupil. It is assumed that some micro-tessellations would thenprovide less, or no, irradiance of the eye pupil. A top hat model wouldbe appropriate to model this case.

Unequal irradiance of eye pupil from multiple micro-tessellations for agiven field angle is investigated. To model this case, an unequalaperture weighting needs to be modeled. For any given single fieldangle, the output from micro-tessellations to micro-tessellations maynot be a smooth function, but rather a step function, as shown in thespatial distribution plots below.

Non-Limiting Working Examples

The modeling that follows firstly evaluated the equal irradiance casefor 25%, 50% and 75% aperture fill. Most field angle cases will not betop hat, and must be evaluated with a representative field angleweighting function for different micro-tessellations.

A typical angular distribution is shown in FIG. 42A. The correspondingspatial distribution is shown in FIG. 42B. In Case A, a top hat functionfor this field angle gives 50% aperture fill. In Case B, the tiles havedifferent weighting. Aperture therefore is not a top hat function. Notethat micro tessellations do not need to be square or in the order asshown and may have any shape or order, such as a 2D distribution.

Structured and random arrangements were investigated. The followingFigures show Non-Random, Regular Repeating Micro-Tessellation Patterns.

FIG. 43 illustrates MTF curves (FIG. 43A) and a 3D layout drawing FIG.43B showing the effects of 50% aperture fill: 50 um apertures on a 100um pitch, 3 mm eye pupil. It was assumed 10 um apertures on 40 um pitch(25% fill factor) and green light (532 nm) only. Note the highmodulation in the resulting frequency space. FIG. 44 shows the effectsof 25% aperture fill: 10 um apertures on 40 um pitch, 3 mm eye pupil.MTF and 3D layout plots are provided. 10 um apertures on 40 um pitch(25% fill factor). Green (532 nm) are assumed. FIG. 45 shows the effects50% aperture fill: 125 um apertures on 250 um pitch, 3 mm eye pupilusing a MTF plot (FIG. 45A) and a footprint diagram (FIG. 45B). 125 umstripe apertures on 250 um pitch (50% fill factor) and Green (532 nm)are assumed. The non-randomized, regular periodic structures exhibitdips in the MTF through out the angular frequency range of interest,typically: 1.4 cyc/mr.

Random Micro-Tessellation Patterns were considered next. Results fromperiodic aperture functions show ‘holes’ in the MTF. The followinginvestigates randomization of the eye pupil fill using microtessellations. Tessellation % fill of 25%, 50% and 75% are considered.For this initial analysis, the tessellation was considered to be 100% ofthe eye pupil. Later cases consider a 1 mm square tessellation thatcontains micro tessellations with a 3 mm eye pupil.

The following illustrations illustrate the characteristics of 50 micronmicro-tessellations. FIG. 46A is a footprint diagram showing the effectof 75% aperture fill of 50 um micro tessellations in 3 mm eye pupil.FIG. 46B is a MTF plot showing the effect of 75% aperture fill of 50 ummicro tessellations in 3 mm eye pupil FIG. 47A is a footprint diagramshowing the effect of 50% aperture fill of 50 um micro tessellations in3 mm eye pupil FIG. 47B is a MTF plot showing the effect of 50% aperturefill of 50 um micro tessellations in 3 mm eye pupil FIG. 48A is afootprint diagram showing the effect of 25% aperture fill of 50 um microtessellations in 3 mm eye pupil FIG. 48B is a MTF plot showing theeffect of 25% aperture fill of 50 um micro tessellations in 3 mm eyepupil.

125 micron micro-tessellation was investigated next. FIG. 49A is afootprint diagram showing the effect of 75% Aperture Fill of 125 ummicro tessellations 3 mm Eye Pupil. FIG. 49B is a footprint diagramshowing the effect of 75% Aperture Fill of 125 um micro tessellations 3mm Eye Pupil. FIG. 50A is a footprint diagram showing the effect of 50%Aperture Fill of 125 um micro tessellations 3 mm Eye Pupil. FIG. 50B isa MTF plot showing the effect of 50% Aperture Fill of 125 um microtessellations 3 mm Eye Pupil. FIG. 51A is a footprint diagram showingthe effect of 25% Aperture Fill of 125 um micro tessellations 3 mm EyePupil. FIG. 51B is a MTF plot showing the effect of 25% Aperture Fill of125 um micro tessellations 3 mm Eye Pupil.

250 micron micro-tessellations were investigated next. FIG. 52A is afootprint diagram showing the effect of 75% Aperture Fill of 250 ummicro tessellations 3 mm Eye Pupil. FIG. 52B is a footprint diagramshowing the effect of 75% Aperture Fill of 250 um micro tessellations 3mm Eye Pupil. FIG. 53A is a footprint diagram showing the effect of 50%Aperture Fill of 250 um micro tessellations 3 mm Eye Pupil. FIG. 53B isa MTF plot showing the effect of 50% Aperture Fill of 250 um microtessellations 3 mm Eye Pupil. FIG. 54A is a footprint diagram showingthe effect of 25% Aperture Fill of 250 um micro tessellations 3 mm EyePupil. FIG. 54B is a MTF plot showing the effect of 25% Aperture Fill of250 um micro tessellations 3 mm Eye Pupil.

Tessellations smaller than the eye pupil diameter and microtessellations were also investigated. FIG. 55A is a footprint diagramshowing the effect of 1 mm tessellation with 50% fill of 125 um microtessellations using 3 mm Eye Pupil Diameter. FIG. 55B is a MTF plotshowing the effect of 1 mm tessellation with 50% fill of 125 um microtessellations using 3 mm Eye Pupil Diameter. FIG. 56A is a footprintdiagram showing the effect of 1.5 mm tessellation with 50% fill of 125um micro tessellations using 3 mm eye pupil diameter. FIG. 56B is afootprint diagram showing the effect of 1 mm tessellation with 50% fillof 125 um micro tessellations using 3 mm eye pupil diameter. FIG. 57A isa footprint diagram showing the effect of 1 mm tessellation with 50%fill of 125 um micro tessellations using 3 mm eye pupil diameter. FIG.57B is a MTF Plot showing the effect of 1 mm tessellation with 50% fillof 125 um micro tessellations using 3 mm eye pupil diameter.

Spatially randomized variable transmission apertures were investigated.The first step is checking the model validity: change from UDAs toBitmap Greyscale Transmission Apertures. Horizontal strips over 1.5 mmaperture (125 μm μTs) in 3 mm diameter eye pupil.

The following modeling techniques were compared: Implement model as UDAs(User Defined Apertures); implement models using bitmap model astransmission aperture. Here bitmap levels are binary. The MTF resultspredicted are identical, so modeling tools equivalent. FIG. 58A shows aMTF plot of a UDA. FIG. 58B shows a Bitmap Aperture Function.

FIG. 59 shows 1.0 mm tessellation using 125 um micro tessellationsrandomly positioned with variable transmission and 3 mm eye pupil. Usinga variable aperture transmissions improves the model to better representnon-top hat model cases (which are the majority of tessellations). DEvalues of 0%, 50% and 100% are equivalent to the field angle case shownin FIG. 59A.

It is noted that this represents the spatially broadest possible case of3 overlapping gratings—i.e., the field angle is output by 75% of theprimary tessellation area (albeit that there is a 50% contribution fromtwo of micro-tessellations). 4 tile types are represented here.Transmission values of each were: 50%; 100%; 50%; 0%. Micro tessellationapertures are 125 um squares. The grid was 8×8 pixels, so thetessellation aperture is 1 mm×1 mm square.

FIG. 60 is a MTF plot showing the effect of 1.0 mm tessellation using125 um μTs randomly positioned with variable transmission and a 3 mm eyepupil. Note that spatial frequencies in the upper boxed region fall inbetween prediction shown in the figures relating to top hat predictionsfor 125 um pixels with 50% and 75% aperture fill). Higher spatialfrequencies shown in the lower boxed region are most affected by theprimary tessellation shape. The reader is referred to the figuresshowing for 50% aperture fill. It should also be noted that there is MTFimprovement for 75% aperture fill.

Referring next to FIG. 61, a 1.5 mm tessellation using 125 um microtessellations randomly positioned with variable transmission and 3 mmeye pupil was considered. Four different tile types are represented inFIG. 61. The transmission values of each were: 50%; 100%; 50%; 0%. Themicro tessellations apertures were 125 um squares. The grid is 12×12pixels, so the tessellation aperture is 1.5 mm×1.5 mm square.

FIG. 62 is a MTF showing the effect of 1.5 mm tessellation using 125 ummicro tessellations randomly positioned with variable transmission and 3mm eye pupil. It should be noted that high spatial frequencies mostaffected by the primary tessellation shape, so increasing underlyingtessellation from 1.0 mm to 1.5 mm improved high frequency response.

In summary:

-   -   a) Diffraction effects of micro tessellations need to be        accounted for.    -   b) Diffraction effects of micro tessellations are distinct from        the diffraction effects of the underlying primary tessellation        pattern.    -   c) Use of μTs degrades MTF compared to that of an single        tessellation that does not contain micro tessellations. However,        micro tessellations enable the tessellation to have a larger        angular bandwidth, thereby reducing the overall number of        tessellations desired. In turn this permits larger        tessellations.    -   d) A regular pattern of μTs will lead to an MTF modulation that        leads to unacceptable dips in the MTF frequency response.    -   e) MTF dips can be averaged out by spatially randomizing the        micro tessellations. Note that the μTs need to be sufficiently        small to permit reasonable randomization. About an 8:1 ratio of        tessellation to μT width appears to be sufficient, although this        has not been explored fully.    -   f) The amount of angular field overlap between tessellations is        crucial to the successful implementation of μTs. In cases        modeled the ABW of micro tessellations is at least half of the        overall tessellation ABW. Greater overlap will lead to improved        MTF performance because this effectively increases the available        aperture for a given field angle.    -   g) Tools are now established to model trade off cases for        different grating configurations.

Implementation of micro-tessellation structures with spatialrandomization across a tessellation provides additional designflexibility. In effect tessellation angular bandwidth (ABW) is enhancedat the expense of MTF. Results show that Randomization of microtessellation features permits homogenization (roughly an averaging) ofMTF oscillations found in non-randomized patterns. Furthermore, MTF atspatial frequencies that are of less interest can be sacrificed forimproved tessellation ABW. Different cases of relevant overlappinggratings need to be considered. The MTF supported by micro-tessellationis dependent on micro-tessellation size and overlapping %. The ABW ofrepresentative cases of overlapping tessellations need to be consideredin more detail, in conjunction with the fold gratings desired to supportthe desired architecture. Micro-tessellations with feature sizes of 50μm, 125 μm and 250 μm have been considered in the context of a 3 mm eyepupil and 0.5 mm, 1.0 mm and <3 mm sized primarily tessellationelements. These are practical numbers to work with in the context of anear eye display. Tessellations may however be any size or shape, andmicro-tessellation may be any size or shape smaller than the primarytessellation.

An Illumination Uniformity Analysis of the tessellation pattern wasconducted next. Referring to FIG. 63, Case 1, which comprises 1 mmtessellations, was considered. The fill per the overlaid referencedesigns in the Figure. FIG. 63 represents 6 layer, 12 tile, monochromereference design. It was assumed a single tile with 50% Aperture Fill.It was further assumed: 17 mm eye relief; 3 mm eye pupil; 6 layermonochrome reference design; 1 mm tessellations, and an offset referencedesign. The unit cell is 2×3. The overlay is shown in the FIG. 63 togenerate the tiled overlay pattern. With 1 mm tessellations, min to maxbest uniformity is +/−12% with 50% aperture fill i.e. +/−12% uniformityvariation=24% p-p.

FIG. 64 shows Case 1 b repeated on axis for a 3 mm eye pupil at 30 mmeye relief. Eye relief impacts the spatial frequency of the variation.The larger eye relief causes higher spatial frequency ripple. Uniformitymagnitude is unaffected. The maximum ripple is 56.6% of pupil fill.Minimum ripple is 43.4% of pupil fill. Uniformity is +/−13.2%, 26.4%peak-to-peak.

FIG. 65 shows Case 2: 1 mm tessellations; fill optimized. The Figuresrepresent a 6 layer, 12 tile monochrome reference design with gratingpositions reoptimized. A single tile has 50% aperture fill. A 3 mm eyepupil and 1 mm tessellations were assumed. The tessellations arespatially uniform.

FIG. 66 illustrates Case 2: consideration of maximum and minimumsituations. Footprint diagrams corresponding to a minimum 45.1% and amaximum 54.9% are shown. With 1 mm tessellations, minimum to maximumbest uniformity is +/−5% with 50% aperture fill, i.e., +/−10% uniformityvariation (20% p-p).

FIG. 67 illustrates Case 3: 0.5 mm tessellations with 50% aperture fill,off axis. FIG. 67 represents a 6 layer, 12 tile, monochrome referencedesign but with 0.5 mm tessellations. A single tile: 50% aperture filland 3 mm eye pupil are assumed. This calculation simulates 50% aperturefill with 0.5 mm wide tessellations. Ripple is calculated as:maximum=50.4; minimum=49.6. Ripple magnitude is about +/−0.8% (1.6%P-P). The field range measured was ˜11 deg to 24 deg. Ripple frequencyis ˜1 cycle for 1.25 deg.

FIG. 68 illustrates Case 3 b: 0.5 mm tessellations with 50% aperturefill, on axis. FIG. 68 represents a 6 layer, 12 tile, monochromereference design but with 0.5 mm tessellations. A single tile: 50%aperture fill; and 3 mm eye pupil were assumed. This simulates 50%aperture fill with 0.5 mm wide tessellations. Ripple was calculated as:maximum=50.9; minimum=49.6. Ripple magnitude is about +/−1.5% (3% P-P).The field range measured was ˜+/−6.5 deg. Off axis, tessellations areforeshortened, and thus uniformity improves. Ripple frequency is ˜1cycle for 1.25 deg.

FIG. 69 illustrates a 4 mm eye pupil, 0.5 mm tessellations, 50% aperturefill. As shown in the drawings the characteristics are: maximum: 51.97%;minimum: 48.03%; and ripple: +/−2% (=4% p-p).

FIG. 70 illustrates a 3 mm eye pupil, 33% aperture fill (3 layers, 9tile types). FIG. 70 represents 3 layer, 9 tile, monochrome referencedesign but with 0.5 mm tessellations. A single tile: 33% Aperture Fill;and a 3 mm eye pupil were assumed. Ripple was calculated at:maximum=36.9; minimum=30.4. Ripple magnitude is ˜6.5%/33%=+/−9.75%(=19.5% P-P). Ripple frequency is ˜1 cycle for 5 deg.

FIG. 71 illustrates a 4 mm eye pupil, 33% aperture fill (3 layers, 9tile types). A single tile: 33% Aperture Fill and 4 mm eye pupil wereassumed. Ripple was calculated as: maximum=35; minimum=30.8. Ripplemagnitude is ˜4.2%/33%=+/−6.3%=12.6% P-P. The ripple frequency is ˜1cycle for 5 deg.

FIG. 72 illustrates a 3 mm eye pupil, 33% aperture fill (3 layers, 9tile types). A single tile: 33% aperture fill and 3 mm eye pupil wereassumed. The computed characteristics are: ripple maximum: 35.2%; rippleminimum: 29.7%; uniformity: 5.5%/33.3%=+/−8.25%=16.5%.

FIG. 73 illustrates how a unit cell forms an evenly distributed pattern.

FIG. 74 is a recalculation of the embodiment using a 4 mm eye pupil, 33%aperture fill (3 layers, 9 tile types). This needs the pattern to have1×3 unit cell, with even columns offset by 0.5 pixel.

A grid distribution using even column half pixel offsets gives a moreeven distribution. The computed characteristics are: ripple maximum:35.0%; ripple minimum: 31.0%; uniformity: 4.0%/33.3%=+/−6%=12%.

FIG. 75 illustrates a 4 mm eye pupil, 33% aperture fill (3 layers, 9tile types). This embodiment needs the pattern to have 1×3 unit cell,with even columns offset by 0.5 pixel.

Grid distribution using even column half pixel offsets gives a more evendistribution. The computed characteristics are: ripple maximum: 34.6%;ripple minimum: 32.7%; uniformity: 1.9%/33.3%=+/−2.85%=5.7%.

A series of reference designs based on micro-tessellation principleshave been developed and are summarised below

-   -   1. Reference design:        -   Monochromatic, 6 layer, 12 tiles (50% aperture fill), 1 mm            tessellations:        -   3 mm eye pupil: 24% uniformity    -   2. Reference design with reoptimized grating locations on        different layers:        -   Monochromatic, 6 layer, 12 tiles (50% aperture fill), 1 mm            tessellations:        -   3 mm eye pupil: 20% uniformity    -   3. Reference design using 0.5 mm tessellations:        -   Monochromatic, 6 layer, 12 tiles (50% aperture fill), 0.5 mm            tessellations:        -   3 mm eye pupil: ˜3% to 2% uniformity across field.    -   4. 3 mm eye pupil (Target: C AR Outdoor)        -   3 layer, 9 tiles (33% aperture fill), 0.5 mm tessellations:        -   Up to 16.5% uniformity    -   5. 4 mm eye pupil [Target: C Movie Indoor]        -   3 layer, 9 tiles (33% aperture fill), 0.5 mm tessellations:        -   Up to 12% uniformity

Achieving 50% aperture fill of a single tile provides significantlyimproved uniformity over even 33% aperture fill (˜5× uniformityimprovement on 3 mm eye pupil). For 50% aperture fill, 0.5 mm performssignificantly better than a 1 mm tessellation: 3% vs. 20% for a 3 mm eyepupil.

50% aperture fill for 9 tiles need ‘4.5’ (i.e., 5 layers).

Eye pupil irradiance uniformity with field angle improves with decreasedprimary tessellation element size and increase primary tessellationelement aperture fill. It is noted that decreased tile type density on agiven layer will then improve the irradiance uniformity with field anglebecause fewer tile types will increase the aperture fill of any singleprimary tessellation element type. Decreased primary tessellationelement size degrades MTF (resolution). It is noted that decreasedprimary tessellation element size, and increased density of a primarytessellation element type permits irregular patterns. This in turnpermits homogenization of MTF of primary tessellations, and theopportunity to vary the irradiance uniformity field angular ripplefrequency. The use of small (micro tessellations) inside the aperture ofa primary tessellation may improve the overall angular bandwidth of aprimary tessellation element, thereby presenting the opportunity toreduce the number of primary tessellation element types desired.

REFERENCES

The following patent applications are incorporated by reference hereinin their entireties:

U.S. Provisional Patent Application No. 61/627,202 with filing date 7Oct. 2011 by the present inventors entitled WIDE ANGLE COLOR HEADMOUNTED DISPLAY which is also referenced by the Applicant's docketnumber SBG106;

PCT Application No.: US2008/001909, with International Filing Date: 22Jul. 2008, entitled LASER ILLUMINATION DEVICE;

PCT Application No.: US2006/043938, entitled METHOD AND APPARATUS FORPROVIDING A TRANSPARENT DISPLAY;

PCT Application No.: PCT/GB2010/001982 entitled COMPACT EDGE ILLUMINATEDEYEGLASS DISPLAY;

PCT Application No.: PCT/GB2010/000835 with International Filing Date:26 Apr. 2010 entitled Compact holographic edge illuminated eyeglassdisplay;

PCT Application No.: PCT/GB2010/002023 filed on 2 Nov. 2010 entitledAPPARATUS FOR REDUCING LASER SPECKLE.

U.S. Patent Application: Ser. No. 10/555,661 filed 4 Nov. 2005 entitledSWITCHABLE VIEWFINDER DISPLAY.

U.S. Provisional Patent Application No. 61/344,748 with filing date 28Sep. 2010 entitled Eye Tracked Holographic Edge Illuminated EyeglassDisplay;

U.S. Provisional Patent Application 61/573,066 with filing date 24 Aug.2011 by the present inventors entitled HOLOGRAPHIC POLYMER DISPERSEDLIQUID CRYSTAL MATERIALS AND DEVICES;

U.S. Provisional Patent Applications No. 61/457,835 with filing date 16Jun. 2011 entitled HOLOGRAPHIC BEAM STEERING DEVICE FOR AUTOSTEREOSCOPICDISPLAYS;

PCT Application No.: US2008/001909, with International Filing Date: 22Jul. 2008, entitled LASER ILLUMINATION DEVICE

PCT Application No.: PCT/GB2010/002023 filed on 2 Nov. 2010 by thepresent inventors entitled APPARATUS FOR REDUCING LASER SPECKLE.

U.S. Provisional Patent Application No. 61/573,121 with filing date 7Sep. 2011 by the present inventors entitled METHOD AND APPARATUS FORSWITCHING HPDLC ARRAY DEVICES which is also referenced by theApplicant's docket number SBG105B;

PCT Application No.: PCT/GB2010/000835 with International Filing Date:26 Apr. 2010 entitled COMPACT HOLOGRAPHIC EDGE ILLUMINATED EYEGLASSDISPLAY (and also referenced by the Applicant's docket numberSBG073PCT);

a U.S. Provisional Patent Application 61/573,082 with filing date 29Aug. 2011 by the present inventors entitled CONTACT IMAGE SENSORS;

U.S. Provisional Patent Application No. 61/573,156 filed on 16 Sep.2011, entitled “Holographic wide angle near eye display” (SBG LabsReference No. SBG106A);

U.S. Provisional Patent Application No. 61/573,175 filed on 19 Sep.2011, entitled “Holographic wide angle near eye display” (SBG LabsReference No. SBG106B);

U.S. Provisional Patent Application No. 61/573,176 filed on 19 Sep.2011, entitled “Holographic wide angle near eye display” (SBG LabsReference No. SBG106C);

U.S. Provisional Patent Application No. 61/573,196 filed on 25 Sep.2011, entitled “Further improvements to holographic wide angle near eyedisplay” (SBG Labs Reference No. SBG106D);

U.S. Provisional Patent Application No. 61/627,202 filed on 7 Oct. 2011,entitled “Wide angle color head mounted display” (SBG Labs Reference No.SBG106);

U.S. Provisional Patent Application No. 61/687,436 filed on 25 Apr.2012, entitled “Improvements to holographic wide angle head mounteddisplay” (SBG Labs Reference No. SBG109);

CONCLUSION

All literature and similar material cited in this application,including, but not limited to, patents, patent applications, articles,books, treatises, and web pages, regardless of the format of suchliterature and similar materials, are expressly incorporated byreference in their entirety. In the event that one or more of theincorporated literature and similar materials differs from orcontradicts this application, including but not limited to definedterms, term usage, described techniques, or the like, this applicationcontrols.

While the present teachings have been described in conjunction withvarious embodiments and examples, it is not intended that the presentteachings be limited to such embodiments or examples. On the contrary,the present teachings encompass various alternatives, modifications, andequivalents, as will be appreciated by those of skill in the art.

While various inventive embodiments have been described and illustratedherein, those of ordinary skill in the art will readily envision avariety of other means and/or structures for performing the functionand/or obtaining the results and/or one or more of the advantagesdescribed herein, and each of such variations and/or modifications isdeemed to be within the scope of the inventive embodiments describedherein. More generally, those skilled in the art will readily appreciatethat all parameters, dimensions, materials, and configurations describedherein are meant to be exemplary and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the inventive teachingsis/are used. Those skilled in the art will recognize many equivalents tothe specific inventive embodiments described herein. It is, therefore,to be understood that the foregoing embodiments are presented by way ofexample only and that, within the scope of the appended claims andequivalents thereto, inventive embodiments may be practiced otherwisethan as specifically described and claimed. Inventive embodiments of thepresent disclosure are directed to each individual feature, system,article, material, kit, and/or method described herein. In addition, anycombination of two or more such features, systems, articles, materials,kits, and/or methods, if such features, systems, articles, materials,kits, and/or methods are not mutually inconsistent, is included withinthe inventive scope of the present disclosure.

Also, the technology described herein may be embodied as a method, ofwhich at least one example has been provided. The acts performed as partof the method may be ordered in any suitable way. Accordingly,embodiments may be constructed in which acts are performed in an orderdifferent than illustrated, which may include performing some actssimultaneously, even though shown as sequential acts in illustrativeembodiments.

All definitions, as defined and used herein, should be understood tocontrol over dictionary definitions, definitions in documentsincorporated by reference, and/or ordinary meanings of the definedterms.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.” Any ranges citedherein are inclusive.

The terms “substantially” and “about” used throughout this Specificationare used to describe and account for small fluctuations. For example,they can refer to less than or equal to ±5%, such as less than or equalto ±2%, such as less than or equal to ±1%, such as less than or equal to±0.5%, such as less than or equal to ±0.2%, such as less than or equalto ±0.1%, such as less than or equal to ±0.05%.

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Multiple elements listed with“and/or” should be construed in the same fashion, i.e., “one or more” ofthe elements so conjoined. Other elements may optionally be presentother than the elements specifically identified by the “and/or” clause,whether related or unrelated to those elements specifically identified.Thus, as a non-limiting example, a reference to “A and/or B”, when usedin conjunction with open-ended language such as “comprising” can refer,in one embodiment, to A only (optionally including elements other thanB); in another embodiment, to B only (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of” “Consisting essentially of,” when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” “composed of,” and the like are tobe understood to be open-ended, i.e., to mean including but not limitedto. Only the transitional phrases “consisting of and” consistingessentially of shall be closed or semi-closed transitional phrases,respectively, as set forth in the United States Patent Office Manual ofPatent Examining Procedures, Section 2111.03.

The claims should not be read as limited to the described order orelements unless stated to that effect. It should be understood thatvarious changes in form and detail may be made by one of ordinary skillin the art without departing from the spirit and scope of the appendedclaims. All embodiments that come within the spirit and scope of thefollowing claims and equivalents thereto are claimed.

What is claimed is:
 1. A waveguide display, comprising: a substratetransparent to visible light; a coupler configured to couple displaylight into the substrate such that the display light propagates withinthe substrate through total internal reflection; a first grating on afirst region of the substrate; and a second grating on a second regionof the substrate, wherein the second region is different from the firstregion, and the second grating overlaps with the first grating in atleast a see-through region of the waveguide display, wherein the firstgrating and second grating are configured to diffract the display lightin at least two different directions.
 2. The waveguide display of claim1, wherein the first grating or the second grating include at least onegrating region comprising different grating prescriptions multiplexedinto the same area, wherein the different grating prescriptions compriseK-vector or surface grating period.
 3. The waveguide display of claim 1,wherein the first grating or the second grating include grating regionscomprising different grating prescriptions multiplexed using spatiallydiscrete grating regions, wherein the different grating prescriptionscomprise K-vector or surface grating period.
 4. The waveguide display ofclaim 1, wherein the first grating or the second grating provide beamexpansion.
 5. The waveguide display of claim 1, wherein the firstgrating or the second grating extract light into an eyebox.
 6. Thewaveguide display of claim 1, wherein the first grating or the secondgrating include at least one grating region with a rolling k-vector. 7.The waveguide display of claim 1, wherein the first grating or thesecond grating includes at least one grating portion configured as anon-switching grating.
 8. The waveguide display of claim 1, wherein thefirst grating or the second grating includes at least one gratingportion configured as a Bragg grating.
 9. The waveguide display of claim1, wherein the first grating or the second grating includes at least onegrating portion configured as a switching grating.
 10. The waveguidedisplay of claim 1, wherein the first grating or the second gratingincludes at least one grating portion configured as a switchable Bragggrating.
 11. The waveguide display of claim 1, wherein the first gratingor the second grating includes at least one grating portion including asurface grating.
 12. The waveguide display of claim 1, wherein a gratingportion of the first grating having a first grating prescriptionoverlaps a grating portion of the second grating having a second gratingprescription, wherein the first grating prescription and/or the secondgrating prescription comprises K-vector or surface grating period. 13.The waveguide display of claim 1, wherein the first grating or thesecond grating include at least one grating portion configured to:provide a beam expansion of the display light; diffract the displaylight in at least two different directions corresponding to at least twodifferent field of view portions; and provide extraction of the displaylight from the waveguide.
 14. The waveguide display of claim 1, whereinthe first grating and the second grating are configured to provide beamexpansion and display light extraction into an eyebox.